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Detection of caffeine intake by means of EC-SERS spectroscopy of human saliva
Abstract
This work presents the application of EC-SERS spectroscopy for the detection of caffeine consumption from human saliva. Caffeine and paraxanthine as the major metabolite of caffeine were tested. Model samples of saliva spiked with caffeine were investigated, and detection of caffeine in real-life saliva samples was tested in order to ensure the viability of the method for clinical applications. Two doses of caffeine (2 mg/kg and 3.5 mg/kg) were ingested by volunteers, and their saliva samples were taken at different time periods ranging from 1 h to 10 h after the consumption. Density functional theory calculations of caffeine and paraxanthine adsorbed on the silver surface were performed in order to better understand the adsorption of the investigated molecules and to make a correct assignment of the experimental spectral bands of the EC-SERS spectra. It was determined that a low dose caffeine consumption can be detected by the appearance of the SERS spectral marker band of caffeine and paraxanthine at 692 cm⁻¹. The intensity of this band is mostly reasoned by the paraxanthine concentration since the intensity changes of the band over time correlates to the concentration changes of paraxanthine determined by the pharmacokinetic studies of paraxanthine and caffeine in the human saliva. It was found that the limit of detection paraxanthine in saliva by means of EC-SERS is as low as 15 μM and can be further improved.
... D'Elia et al., [11] while studying saliva and cocaine, avoid any pretreatment steps by transferring saliva to NMR tubes directly before resonant Raman analysis, an approach <10,000 [48,96,125,196,200,203,219,224,232,241,244,254,255] 10,000 [97,103,220,221,223,227,256] >10,000 [60,[98][99][100]131,193,202,204,217,218,222,257,258] Centrifuge time 1-2 min [96,232,256] 5 mins [60,193] 10 mins [48,[97][98][99][100]103,131,202,204,[217][218][219][220][221]223,224,227,254] 10-40 mins [125,196,200,203,222,241,244,255,257] Filtering Methanol [48,203] Acetonitrile [244] Acetic acid [137] Chloroform [256] Syringe filter [47] (0.2 lm diameter) Membrane [214] (0.45 lm pore diameter) [241] (0.22 lm pore diameter) Storage temp 4 C [48,98,107,188,196,203,[213][214][215][216]219] À20 C [60,197,217,230] À80 C [83,96,103,189,202,[221][222][223][224]227,232,239] Liquid Nitrogen [97,220] which may be more applicable for real-world portable sensors where point-of-need saliva samples cannot be easily or rapidly processed. This approach, however, significantly compromises signal intensity and the resultant LoD of 10 lg/mL is three orders of magnitude above the requisite forensic specification. ...
... [307] Intricately patterned top-down fabricated SERS substrates [308][309][310][311][312][313] and inexpensive, high sensitivity, bottom-up SERS platforms [113,[314][315][316][317][318][319][320][321][322][323][324][325] have been emerging, building upon the significant advances in nano-fabrication technologies. [309,326,327] Alternative approaches also exist, for instance, Su et al. [256] use large AuNP clusters ( Figure 6A), and recently, Veli cka et al. [258] have used an electrochemical SERS silver electrode set-up to detect caffeine in saliva. SERS is viewed as a promising route to accelerate the adoption of Raman spectroscopy for biostudies. ...
The use of Raman spectroscopy combined with saliva is an exciting emerging spectroscopy-biofluid combination. In this review, we summarize current methods employed in such studies, in particular the collection, pretreatment, and storage of saliva, as well as measurement procedures and Raman parameters used. Given the need for sensitive detection, surface-enhanced Raman methods are also surveyed, alongside chemometric techniques. A meta-analysis of variables is compiled. We observe a wide range of approaches and conclude that standardization of methods and progress to more extensive validation Raman-saliva studies is necessary. Nevertheless, the studies show tremendous promise toward the improvement of speed, diagnostic accuracy, and portable device possibilities in applications such as healthcare, law enforcement, and forensics.
... This is believed to be due to individual characteristics and genetic polymorphisms related to the activity of the CYP1A2 isoform of the P-450 cytochrome, involved in substance metabolism [74,84]. Caffeine presence can also be assessed by analyzing urine, cerebrospinal fluid, saliva, bile, dental calculus, and tissue fragments, such as kidney or spleen [74,81,[95][96][97][98]. Additionally, when analyzing cases of deaths due to energy drink overdose, it is crucial to collect witness reports regarding the victim's symptoms and analyze the scene of the incident to search for elements indicating intensive consumption, such as empty cans of drinks. ...
Introduction and objective:
The number of users of energy drinks and caffeine shots worldwide is very high and varies depending on the age group. In many countries, legislative measures have been taken to restrict access to these products for minors. The main ingredient in energy boosters is caffeine which is responsible for the stimulating properties of these products. Other substances, such as guarana, taurine, vitamins, and simple sugars, are also included in their composition. The aim of the study is to investigate the impact of these products on the body, and their medical and forensic aspects.
Review methods:
A literature review was conducted using PubMed, Medline, Google Scholar, and information from legal documents and product labels available on the market.
Brief description of the state of knowledge:
The use of high-caffeine products is associated with a negative impact on various systems in the human body, with cardiovascular issues being the most commonly observed. Based on available literature, it can be speculated that children are most vulnerable to the harmful effects of these substances. Another concern related to energy drinks and caffeine shots is their interaction with many medications and other substances. There have been cases reported of overdosing on energy drinks, suicide attempts, and deaths, as a result. In medico-legal diagnostics, toxicological examinations regarding caffeine levels in the blood and appropriate differential diagnostics are crucial.
Summary:
The consumption of energy drinks and caffeine shots may pose a threat to health. Further analyses of the broad impact of these products on the human body, with special consideration for children, are needed.
... Thus, the -0.7 V (vs Ag/AgCl) was selected to carry out further EC-SERS measurements. Several studies reported that the change of the electrode potential may result in the change of the coverage and/or the adsorption orientation of the molecule, resulting in changes in the SERS intensity [29,47,48]. In this study, we speculated that the potential dependence of peak intensity was due to the changes in the interaction between the substrate surface and molecules. ...
Acetamiprid (AAP) is a common neonicotinoid pesticide and their residues have emerged as a widely concerned issue on vegetables and fruits. In this work, a facile electrochemical surface-enhanced Raman spectroscopy (EC-SERS) method with one step of "mixing and detection" was proposed for detection of AAP. Wherein, screen printed electrode (SPE) was modified by dropping silver nanoparticles (AgNPs) onto the SPE surface. Compared to the normal SERS detection, the EC-SERS had a 5-fold enhancement in SERS signal with an applied potential at-0.7 V. Under the optimal applied potential, a wide linear range from 0.1 μM to 1000 μM was achieved with a low limit of detection (LOD, 0.04 μM), about 7-fold lower than that of the normal SERS method (LOD, 0.31 μM). Density functional theory (DFT) calculation revealed that the van der Waals force between AAP molecules and AgNPs was greatly enhanced. Besides, the EC-SERS method was successfully applied for the detection of AAP in Brassica chinensis L., and the results correlated well (R 2 =0.9760) with those obtained from liquid chromatography-tandem mass spectrometry (HPLC-MS). The proposed method featured in easy operation, rapid detection and high sensitivity, which can act as a promising tool for monitoring pesticide residues in food samples.
... In this study, the drug caffeine was selected as a probe molecule to evaluate this sensor, as it generates a strong SERS response at 785 nm. The SERS of caffeine has been reported for various substrates, mostly silver colloids in water, in extracts from tea and coffee, and in biofluids [24][25][26][27][28][29][30][31][32][33][34][35]. Caffeine SERS has been measured and reported at 1 ppb on silver colloids [24] and 100 ppm on gold colloids [28]. ...
We used surface-enhanced Raman spectroscopy (SERS) for the rapid and sensitive detection and quantification of caffeine in solution. Such a technique incorporated into a portable device is finding wide applications in trace chemical analysis in various fields, including law enforcement, medicine, environmental monitoring, and food quality control. To realize such applications, we are currently developing portable and handheld trace chemical analyzers based on SERS, which are integrated with a sensor embedded with activated gold nanoparticles in a porous glass matrix. In this study, we used this gold SERS-active substrate to measure aqueous solutions of the drug caffeine as a test chemical to benchmark sensor performance by defining sensitivity (lowest measured concentration (LMC) and estimated limit of detection (LOD)), determining concentration dependence and quantification capabilities by constructing calibration curves; by evaluating the effects of pH values of 3, 7, and 11; and by examining the reproducibility of the SERS measurements. The results demonstrate that the SERS sensor is sensitive, with caffeine detected at an LMC of 50 parts per billion (ppb) with an LOD of 0.63 ppb. The results further show that the sensor is very stable and can be used to make reproducible measurements, even under extremely acidic to basic pH conditions. Vibrational assignments of all observed SERS peaks are made and reported for the first time for caffeine on a gold substrate.
... It has been reported that caffeine as well as its major metabolite paraxanthine could be detected via EC-SERS. [114] Then, density functional theory (DFT) calculations were performed on the caffeine and paraxanthines in the saliva sample to further study the adsorption of biomolecules and assign each Raman band. The bands were determined to be related to paraxanthines (Fig. 5D), confirmed by the pharmacokinetic study of paraxanthine and caffeine in human saliva. ...
Metabolites are important biomarkers in human body fluids, conveying direct information of cellular activities and physical conditions. Metabolite detection has long been a research hotspot in the field of biology and medicine. Surface-enhanced Raman spectroscopy (SERS), based on the molecular “fingerprint” of Raman spectrum and the enormous signal enhancement (down to a single-molecule level) by plasmonic nanomaterials, has proven to be a novel and powerful tool for metabolite detection. SERS provides favorable properties such as ultra-sensitive, label-free, rapid, specific, and non-destructive detection process. In this review, we summarized the progress in recent 10 years on SERS-based sensing of endogenous metabolites at the cellular level, in tissues, and in biofluids, as well as drug metabolites in biofluids. We made detailed discussions on the challenges and optimization methods of SERS technique in metabolite detection. The combination of SERS with modern biomedical technology were also anticipated.
Herein, an unprecedented cadmium-based metal–organic framework (JNU-106) fabricated by utilizing pyrazole-functionalized tetraphenylethylene ligands (Py-TPE) and rod-shaped secondary building units is reported, possessing a new (3,3,3,6,6,8)-connected topological network. Thanks to the ingeniously designed intramolecular charge transfer behavior, which originates from the congruent coplanarity between Py and TPE, JNU-106 exhibits intense green luminescence with a quantum yield increased by 1.5 times. The phenomenon of remarkable fluorescence quenching of JNU-106 reveals that it possesses extremely high anti-interference performance, superior sensitivity, and dedicated selectivity toward tetracycline antibiotics (TCAs) in aqueous solutions, which are comparable to those of the state-of-the-art porous sensing compounds. Taking the theoretical calculations and experimental results into account, the luminescence quenching is mainly attributed to the internal filtration effect and the static quenching effect. Considering the portable and rapid performance of JNU-106-based testing strips for sensing TCAs, the fabricated JNU-106 provides an alternative for ecological monitoring and environmental governance.
Applications and advances in surface‐enhanced Raman spectroscopy (SERS) have grown over the last several years, demonstrating improvements in sensitivity and selectivity. Applications for SERS‐related techniques have been explored in many analytical disciplines including forensic applications. Drug chemistry and toxicology may benefit from the growth of SERS since many methods have demonstrated high sensitivity, potential for quantitative analysis, and portable instrumentation for onsite testing. SERS techniques have been developed using many substrates including nanoparticles and colloids; microfluidic devices; paper‐based substrates; electrodes; and wearable/flexible devices. These methods take advantage of the SERS phenomenon, providing more potential applications for Raman analysis and overcoming the traditional challenges of the technique. This is desirable for forensic drug chemistry applications which require screening and confirmatory approaches and analysis of mixtures with low weight percent contributions of analytes, as well as forensic toxicology, where matrix interferences, sensitivity requirements, and a growing introduction of novel drug entities pose challenges. Several chemometric approaches have been applied to Raman data to improve identification, classification, and quantification. These advances position SERS for incorporation into forensic chemistry laboratories. While some SERS applications are available commercially, widespread use of SERS in practicing forensic laboratories remains limited. Due to the requirements for use of analytical techniques in the courtroom, future studies for SERS should revolve around the assessment of validation parameters common in other analytical methods. SERS techniques that are rapid, simple, and inexpensive may be more quickly adapted for forensic testing, where use as advanced screening techniques is a clear avenue of research.
This article is categorized under: Forensic Chemistry and Trace Evidence > Controlled and Emerging Drug Compounds
Toxicology > New Psychoactive Substances
Forensic Chemistry and Trace Evidence > Emerging Technologies and Methods
Thiabendazole (TBZ), a benzimidazole fungicide used for post-harvest treatment, may be a trace contaminant of food matrices. In this work, we report the first EC-SERS (electrochemical-surface enhanced Raman spectroscopy) detection of TBZ in spiked apple juice using electrochemically (EC) roughened, gold-based screen-printed electrodes (AuSPEs) and portable instrumentation. Polarizing the substrate (−0.8V vs. Ag/AgCl) improves the recorded SERS signal of TBZ, allowing to reach a limit of detection (LOD) in juice of 0.061 ppm with a relatively wide linear range (0.5 - 10 μM) and good intermediate precision (%RSD < 10). The recovery of TBZ from unprocessed juice was found to be more than 82%. Furthermore, a proof-of-concept integration of AuSPEs with a miniaturized flow cell for the preconcentration of TBZ and the controlled delivery of sample and reagents has been demonstrated. This approach paves the way for integrated, portable analytical systems applicable for on-site sample collection, processing, and analysis.
This work demonstrates an original and ultrasensitive approach for surface‐enhanced Raman spectroscopy (SERS) detection based on evaporation of self‐lubricating drops containing silver supraparticles. The developed method detects an extremely low concentration of analyte that is enriched and concentrated on sensitive SERS sites of the compact supraparticles formed from drop evaporation. A low limit of detection of 10−16 m is achieved for a model hydrophobic compound rhodamine 6G (R6G). The quantitative analysis of R6G concentration is obtained from 10−5 to 10−11 m. In addition, for a model micro‐pollutant in water triclosan, the detection limit of 10−6 m is achieved by using microliter sample solutions. The intensity of SERS detection in this approach is robust to the dispersity of the nanoparticles in the drop but became stronger after a longer drying time. The ultrasensitive detection mechanism is the sequential process of concentration, extraction, and absorption of the analyte during evaporation of self‐lubrication drop and hot spot generation for intensification of SERS signals. This novel approach for sample preparation in ultrasensitive SERS detection can be applied to the detection of chemical and biological signatures in areas such as environment monitoring, food safety, and biomedical diagnostics. A combination of extraction of the analytes, microdroplet‐templated porous supraparticles, and self‐lubrication of colloidal ouzo drop evaporation is employed for ultra‐sensitive SERS detection. The approach overcomes long‐standing limitations of the coffee‐stain effect to accumulate the analytes to the hotspots of supraparticles. The ultralow detection of limitation is demonstrated for several model compound solutions and caffeine in saliva samples.
Historically, electrochemical surface-enhanced Raman spectroscopy (EC-SERS) was the first format of SERS analysis; however, it is also the least frequently used SERS format for routine analysis. A key advantage of the EC-SERS analysis is the ability to regulate analyte adsorption-desorption by electrode polarization providing additional control over analytical signal and allowing for fast and easy fabrication, cleaning, and regeneration of SERS-active surface. Therefore, this review aims to collect the best examples of analytical reports on the topic and analyze analytical performance of EC-SERS assays to highlight the problems that limit its practical application. The review discusses general design of EC-SERS setup and the factors influencing the potential of maximal SERS signal; standard and advanced formats of EC-SERS analysis; figures of merit, selectivity, critical limitations, and perspective directions. The analytically useful factors are discussed in more detail: specific physicochemical effects, “memory effects” and reusability problems, side electrochemical reactions, and limited selectivity.
Therapeutic drug monitoring (TDM) is an essential clinical practice for optimizing drug dosing, thereby preventing adverse effects of drugs with a narrow therapeutic window, slow clearance, or high interperson pharmacokinetic variability. Monitoring methotrexate (MTX) during high-dose MTX (HD-MTX) therapy is necessary to avoid potentially fatal side effects caused by delayed elimination. Despite the efficacy of HD-MTX treatment, its clinical application in resource-limited settings is constrained due to the relatively high cost and time of analysis with conventional analysis methods. In this work, we developed (i) an electrochemically assisted surface-enhanced Raman spectroscopy (SERS) method for detecting MTX in human serum at a clinically relevant concentration range and (ii) a benchtop, Raman detection system with an integrated potentiostat, software, and data analysis unit that enables mapping of small areas of SERS substrates and quantitative SERS-based analysis. In the assay, by promoting electrostatic attraction between gold-coated nanopillar SERS substrates and MTX molecules in aqueous samples, a detection limit of 0.13 μM with a linear range of 0.43-2 μM was achieved in PBS. The implemented sample cleanup through gel filtration proved to be highly effective, resulting in a similar detection limit (0.55 μM) and linear range (1.81-5 μM) for both PBS and serum. The developed and optimized assay could also be used on the in-house built, Raman device. We showed that MTX detection can be carried out in less than 30 min with the Raman device, paving the way toward the TDM of MTX at the point-of-need and in resource-limited environments.
One of the lessons we learned from the COVID-19 pandemic is that the need for ultrasensitive detection systems is now more critical than ever. While sensors' sensitivity, portability, selectivity, and low cost are crucial, new ways to couple synergistic methods enable the highest performance levels. This review article critically discusses the synergetic combinations of optical and electrochemical methods. We also discuss three key application fields-energy, biomedicine, and environment. Finally, we selected the most promising approaches and examples, the open challenges in sensing, and ways to overcome them. We expect this work to set a clear reference for developing and understanding strategies, pros and cons of different combinations of electrochemical and optical sensors integrated into a single device.
Sample preparation is considered the bottleneck step in bioanalysis because each biological matrix has its own unique challenges and complexity. Competent sample preparation to extract the desired analytes and remove redundant components is a crucial step in each bioanalytical approach. The matrix effect is a key hurdle in bioanalytical sample preparation, which has gained extensive consideration. Novel sample preparation techniques have advantages over classical techniques in terms of accuracy, automation, ease of sample preparation, storage, and shipment and have become increasingly popular over the past decade. Our objective is to provide a broad outline of current developments in various bioanalytical sample preparation techniques in chromatographic and spectroscopic examinations. In addition, how these techniques have gained considerable attention over the past decade in bioanalytical research is mentioned with preferred examples. Modern trends in bioanalytical sample preparation techniques, including sorbent-based microextraction techniques, are primarily emphasized.
The discovery of surface enhanced Raman scattering (SERS) from an electrochemical (EC)-SERS experiment is known as a historic breakthrough. Five decades have passed and Raman spectroelectrochemistry (SEC) has developed into a common characterization tool that provides information about the electrode–electrolyte interface. Recently, this technique has been successfully explored for analytical purposes. EC was found to highly improve the performances of SERS sensors, providing, among others, controlled adsorption of analytes and increased reproducibility. In this review, we highlight the potential of EC-SERS sensors to be implemented for point-of-need (PON) analyses as miniaturized devices, and their ability to revolutionize fields like quality control, diagnosis or environmental and food safety. Important developments have been achieved in Raman spectroelectrochemistry, which now represents a promising alternative to conventional analytical methods and interests more and more researchers. The studies included in this review open endless possibilities for real-life EC-SERS analytical applications.
Biological effects of low-dose ionizing radiation (IR) have been unclear until now. Saliva, because of the ease of collection, could be valuable in studying low-dose IR effects by means of surface-enhanced Raman spectroscopy (SERS). The objective of our study was to compare the salivary SER spectra recorded before and after low-dose IR exposure in the case of pediatric patients (PP). Unstimulated saliva was collected from ten PP before and after irradiation with a cone beam computed tomography (CBCT) machine used for diagnostic purposes. The SERS measurements have been recorded on dried saliva samples using a solid nanosilver plasmonic substrate synthesized using an original method developed in our laboratory. The experimental results showed that salivary SER spectra are dominated by three vibrational bands (441,735 and 2107 cm⁻¹) that can be assigned to bending and stretching vibrations of salivary thiocyanate (SCN-). After exposure, an immediate increase of vibrational bands assigned to SCN- has been recorded in the case of all samples, probably as a result of IR interaction with oral cavity. This finding suggests that SCN- could be used as a valuable biomarker for the detection and identification of low-dose radiation effects.
Epigenetic biomarkers are powerful tools for early disease detection and are particularly useful for elusive conditions like preeclampsia. Predicting preeclampsia at an early stage is one of the most important goals of maternal-fetal medicine. To this end, recent studies have identified microRNAs-such as microRNA-17-as early biomarkers for preeclampsia. Yet clinical applications are lagging, owing in part to the sensing challenges presented by the biomarkers' small size and complex environment. Surface enhanced Raman spectroscopy (SERS) is an emergent optical technique that is recognized for its potential to overcome these challenges. In this study, DNA functionalized nanoparticles were designed as probes to capture and quantify miRNA-17 in solution. SERS was used to determine the presence and concentration of miRNA-17 based on the formation of plasmonic nanoparticle aggregates. The miRNA-17 assay was tested at concentrations of 1 pM to 1 nM in both PBS and a representative complex biological sample. In both situations the assay was unaffected by non-complementary microRNA samples. These results demonstrate SERS's specificity and sensitivity for a new biomarker (miRNA-17) that may ultimately be used in a detection platform for early diagnosis of preeclampsia.
A correct estimate of ligand binding modes and a ratio of their occupancies is crucial for calculations of binding free energies. The newly developed method BLUES combines molecular dynamics with non-equilibrium Candidate Monte Carlo. Non-equilibrium candidate Monte Carlo generates a plethora of possible binding modes and molecular dynamics enables the system to relax. We used BLUES to investigate binding modes of caffeine in the active site of its metabolizing enzyme Cytochrome P450 1A2, with the aim of elucidating metabolite-formation profiles at different concentrations. Because the activation energies for all sites of metabolism do not show a clear preference for one metabolite over the others, the orientations in the active site must play a key role. In simulations with caffeine located in a spacious pocket above the I-helix, it points N3 and N1 to the heme iron, while in simulations where caffeine is in close proximity to the heme, N7 and C8 are preferably oriented towards the heme iron. We propose a mechanism where at low caffeine concentrations caffeine binds to the upper part of the active site, leading to formation of the main metabolite paraxanthine. On the other hand, at high concentrations, two molecules are located in the active site, forcing one molecule into close proximity to the heme and yielding metabolites theophylline and trimethyluretic acid. Our results offer an explanation of previously published experimental results.
Surface-enhanced Raman scattering (SERS) has become a powerful tool in chemical, material and life sciences, owing to its intrinsic features (i.e., fingerprint recognition capabilities and high sensitivity) and to the technological advancements that have lowered the cost of the instruments and improved their sensitivity and user-friendliness. We provide an overview of the most significant aspects of SERS. First, the phenomena at the basis of the SERS amplification are described. Then, the measurement of the enhancement and the key factors that determine it (the materials, the hot spots, and the analyte-surface distance) are discussed. A section is dedicated to the analysis of the relevant factors for the choice of the excitation wavelength in a SERS experiment. Several types of substrates and fabrication methods are illustrated, along with some examples of the coupling of SERS with separation and capturing techniques. Finally, a representative selection of applications in the biomedical field, with direct and indirect protocols, is provided. We intentionally avoided using a highly technical language and, whenever possible, intuitive explanations of the involved phenomena are provided, in order to make this review suitable to scientists with different degrees of specialization in this field.
Traditional tissue biopsy is limited in understanding heterogeneity and dynamic evolution of tumors. Instead, analyzing circulating cancer markers in various body fluids, commonly referred to as “liquid biopsy”, has recently attracted remarkable interest for their great potential to be applied in non-invasive early cancer screening, tumor progression monitoring and therapy response assessment. Among the various approaches developed for liquid biopsy analysis, surface-enhanced Raman spectroscopy (SERS) has emerged as one of the most powerful techniques based on its high sensitivity, specificity, tremendous spectral multiplexing capacity for simultaneous target detection, as well as its unique capability for obtaining intrinsic fingerprint spectra of biomolecules. In this review, we will first briefly explain the mechanism of SERS, and then introduce recently reported SERS-based techniques for detection of circulating cancer markers including circulating tumor cells, exosomes, circulating tumor DNAs, microRNAs and cancer-related proteins. Cancer diagnosis based on SERS analysis of bulk body fluids will also be included. In the end, we will summarize the “state of the art” technologies of SERS-based platforms and discuss the challenges of translating them into clinical settings.
Vibrational spectroscopy offers a unique opportunity to investigate the composition of unknown substances on a molecular basis. The spectroscopy of molecular vibrations using mid-infrared or Raman techniques has been applied to samples of body fluids. This review presents some applications related to body fluids published in the period 2005-2015.
Accurate quantitative measurement of drugs and their metabolites is important as this can be used to establish long-term abuse of illicit materials as well as establish accurate drug dosing for legal therapeutics. However, the levels of drugs and xenometabolites found in human body fluids necessitate methods that are highly sensitive as well as reproducible with the potential for portability. Raman spectroscopy does offer excellent reproducibility, portability and chemical specificity, but unfortunately, the Raman effect is generally too weak unless it is enhanced. We therefore developed surface-enhanced Raman scattering (SERS) and combined it with the powerful machine learning technique of artificial neural networks to enable rapid quantification of caffeine and its two major metabolites theobromine and paraxanthine. We established a three-way mixture analysis from 10−5 to 10−7 mol/dm3, and excellent predictions were generated for all three analytes in tertiary mixtures. The range we selected reflects the levels found in human body fluids, and the typical errors for our portable SERS analysis were 1.7 × 10−6 mol/dm3 for caffeine, 8.8 × 10−7 mol/dm3 for theobromine and 9.6 × 10−7 mol/dm3 for paraxanthine. We believe this demonstrates the exciting prospect of using SERS for the quantitative analysis of multiple analytes simultaneously without recourse to lengthy and time-consuming chromatography, a method that often has to be combined with mass spectrometry.
Electronic supplementary material
The online version of this article (doi:10.1007/s00216-015-9004-8) contains supplementary material, which is available to authorized users.
In clinical practice, one objective is to obtain diagnostic information while minimizing the invasiveness of the tests and the pain for the patients. To this end, tests based on the interaction of light with readily available biofluids including blood, urine, or saliva are highly desirable. In this review we examine the state of the art regarding the use of surface-enhanced Raman spectroscopy (SERS) to investigate biofluids, focusing on diagnostic applications. First, a critical evaluation of the experimental aspects involved in the collection of SERS spectra is presented; different substrate types are introduced, with a clear distinction between colloidal and non-colloidal metal nanostructures. Then the effect of the excitation wavelength is discussed, along with anomalous bands and artifacts which might affect SERS spectra of biofluids. The central part of the review examines the literature available on the SERS spectra of blood, plasma, serum, urine, saliva, tears, and semen. Finally, diagnostic applications are critically discussed in the context of the published evidence; this section clearly reveals that SERS of biofluids is most promising as a rapid, cheap, and non-invasive tool for mass screening for cancer.
The localized surface plasmon resonance (LSPR) of aluminum nanospheres, nanorods, and nanodisks was studied using the finite-difference time-domain (FDTD) method. From the simulation results, optimal dimensions of nanospheres, nanodisks, and nanorods for refractive index sensitivity (RIS), line shape broadening (FWHM), and figure-of-merit (FOM) are calculated for aluminum-based plasmonic nanosensors. Our calculated results show that aluminum is an efficient plasmonic material for refractive index sensing from deep-UV to near infrared wavelengths. The RIS of aluminum nanospheres of optimal size is greater than gold and silver nanospheres. Further, RIS or FOM can be optimized in different spectral region by varying shape and dimensions. The optimization reveals higher FOM for nanospheres in the deep-UV region and for nanorods and nanodisks in the broad visible-NIR region.
Background
The Avogadro project has developed an advanced molecule editor and visualizer designed for cross-platform use in computational chemistry, molecular modeling, bioinformatics, materials science, and related areas. It offers flexible, high quality rendering, and a powerful plugin architecture. Typical uses include building molecular structures, formatting input files, and analyzing output of a wide variety of computational chemistry packages. By using the CML file format as its native document type, Avogadro seeks to enhance the semantic accessibility of chemical data types.
Results
The work presented here details the Avogadro library, which is a framework providing a code library and application programming interface (API) with three-dimensional visualization capabilities; and has direct applications to research and education in the fields of chemistry, physics, materials science, and biology. The Avogadro application provides a rich graphical interface using dynamically loaded plugins through the library itself. The application and library can each be extended by implementing a plugin module in C++ or Python to explore different visualization techniques, build/manipulate molecular structures, and interact with other programs. We describe some example extensions, one which uses a genetic algorithm to find stable crystal structures, and one which interfaces with the PackMol program to create packed, solvated structures for molecular dynamics simulations. The 1.0 release series of Avogadro is the main focus of the results discussed here.
Conclusions
Avogadro offers a semantic chemical builder and platform for visualization and analysis. For users, it offers an easy-to-use builder, integrated support for downloading from common databases such as PubChem and the Protein Data Bank, extracting chemical data from a wide variety of formats, including computational chemistry output, and native, semantic support for the CML file format. For developers, it can be easily extended via a powerful plugin mechanism to support new features in organic chemistry, inorganic complexes, drug design, materials, biomolecules, and simulations. Avogadro is freely available under an open-source license from
http://avogadro.openmolecules.net.
Caffeine concentrations in plasma and saliva were measured by HPLC in 12 healthy subjects after a single oral dose of 250 to 350 mg. There was a linear relationship between caffeine concentrations in the two fluids. Mean (+/- SE) saliva: total plasma concentration ratio was 0.79 +/- 0.02, while the ratio of the free (non-protein bound):total concentration of drug in plasma was 0.59 +/- 0.01. We postulate that the higher saliva:total plasma ratio as compared to the plasma free: total ratio is a result of pH partitioning. The mean elimination t 1/2 estimated from plasma and saliva concentration-time curves were much the same (5.7 +/- 0.7 and 5.9 +/- 0.8 hr). Values for total body clearance and apparent volume of distribution obtained from saliva data were higher than values derived from plasma concentrations. These differences could be corrected by multiplying the saliva-derived parameters by the saliva: total plasma concentration ratio. We conclude that saliva sampling could serve as a useful technique for therapeutic drug monitoring as well as for research of caffeine kinetics when many samples are required.
Drug testing, commonly used in health care, workplace, and criminal settings, has become widespread during the past decade. Urine drug screens have been the most common method for analysis because of ease of sampling. The simplicity of use and access to rapid results have increased demand for and use of immunoassays; however, these assays are not perfect. False-positive results of immunoassays can lead to serious medical or social consequences if results are not confirmed by secondary analysis, such as gas chromatography-mass spectrometry. The Department of Health and Human Services' guidelines for the workplace require testing for the following 5 substances: amphetamines, cannabinoids, cocaine, opiates, and phencyclidine. This article discusses potential false-positive results and false-negative results that occur with immunoassays of these substances and with alcohol, benzodiazepines, and tricyclic antidepressants. Other pitfalls, such as adulteration, substitution, and dilution of urine samples, are discussed. Pragmatic concepts summarized in this article should minimize the potential risks of misinterpreting urine drug screens.
We present a detailed computational analysis of UV/Vis spectra of caffeine, paraxanthine and theophylline in aqueous solution. A hierarchy of solvation approaches for modeling the aqueous environment is tested, ranging from continuum Model to non-polarizable and polarizable Quantum Mechanical(QM)/Molecular Mechanics (MM) models, with and without the explicit inclusion of water molecules in the QM portion. Computed results are directly compared with experimental data, so to highlight the role of electrostatic, polarization and hydrogen boding solute-solvent interactions.
Chromatographic method has long been recognized as the most widely used separation method in bioanalytical research. However, the relatively low sensitivity of existing chromatographic methods remains a significant challenge, as the requirements for experimental procedures become more demanding. This review discussed the main causes for the low sensitivity of chromatographic methods and aimed to introduce different technologies for enhancing their sensitivity in the following aspects. (i) Different pretreatment methods for improving clean‐up efficiency and recovery; (ii) derivatization step for altering the chromatographic behavior of analytes and enhancing MS ionization efficiency; (iii) optimal LC‐MS conditions and appropriate separation mechanism; and (iv) applications of other chromatographic methods, including miniaturized LC, 2D‐LC, 2D‐GC and SFC. Altogether, this study is devoted to summarize the recent technologies reported in the literature and provide new strategies for the detection of bioanalytes.
The number of Americans dying from drug overdoses has risen rapidly, but the contribution of nonopioid drugs to this growth is not well understood. Using vital statistics data from the universe of deaths among US residents in the period 1999-2016, I calculated levels of and increases in overall nonopioid fatal overdose rates and those for subgroups stratified by manner of death, sex, race/ethnicity, and age. Mortality rates were also calculated separately for sedatives, stimulants, antidepressants, and cocaine. Recently developed methods were used to correct for the incomplete reporting of drug involvement on death certificates. From 1999 to 2016 the number of nonopioid drug deaths rose 274 percent, and deaths per 100,000 population rose by 223 percent. Over the same period, opioid-involved fatality counts and rates grew by 371 percent and 307 percent, respectively. Fatal overdose rates involving stimulants increased more than tenfold, with slower growth but higher rates for deaths involving sedatives and cocaine. Midlife non-Hispanic whites generally experienced the highest levels and rise in nonopioid death rates, but cocaine fatality rates were particularly common among nonwhite or Hispanic males ages 40-59. Policies designed to curb the opioid epidemic are probably helpful in reducing nonopioid deaths, but targeted interventions may also be needed.
Vibrational spectroscopy techniques such as Raman and IR (infrared) allow real-time, non-invasive and non-destructiveanalysis of organic compounds with good limit-of-detection. This study aims to show the progress of clinical diagnosis and prognosis due to advances of vibrational spectroscopy techniques in biofluids through extensive literature review. This review was performed by searching for studies using the keywords "biofluids or biological fluids" and "diagnostic techniques" in PubMed, Scopus and Google Scholar. We found580 articles in the 1990s, 1171 articles in the 2000s and 1688 in the years from of 2011. Also, a second search including "biofluids or biological fluids" and "vibrational spectroscopy" returned only one article in the 1990s, three papers in the 2000s and 18 in the years from 2011.This growthsuggests agreat potential of biofluidicresearchusing vibrational spectroscopy. Sample collection variations(quantity and contaminations due to contact with other body parts and their secretions) are important factors that influence sample composition. Once these factors are taken into account, spectroscopic analysis can provide the necessary information to identify a disease, lesion, tumor or infection. With the present review we aim to encourage the researchers concern the study of vibrational spectroscopy techniques for analysis biofluids focusing in clinical applications. In the future, it will benefits for the clinicians, using new diagnostic approaches, and for the patients to have an early diagnostic for every disease.
We previously published a comprehensive review paper reviewing the Raman spectroscopy of biological molecules. This research area has expanded rapidly, which warranted an update to the existing review paper by adding the recently reported studies in literature. This article reviews some of the recent advances of Raman spectroscopy in relation to biomedical applications starting from natural tissues to cancer biology. Raman spectroscopy, an optical molecular detective, is a vibrational spectroscopic technique that has potential not only in cancer diagnosis but also in understanding progression of the disease. This article summarizes some of the most widely observed peak frequencies and their assignments. The aim of this review is to develop a database of molecular fingerprints, which will facilitate researchers in identifying the chemical structure of the biological tissues including most of the significant peaks reported both in the normal and cancerous tissues. It has covered a variety of Raman approaches and its quantitative and qualitative biochemical information. In addition, it covers the use of Raman spectroscopy to analyse a variety of different malignancies including breast, brain, cervical, gastrointestinal, lung, oral, and skin cancer. Multivariate analysis approaches used in these studies have also been covered.
Keywords: Raman spectroscopy, biological tissues, analysis of cancer tissues, characteristic peak assignments
Early disease diagnosis is crucial for timely and effective healthcare monitoring and treatment. Demand for modern point-of-care (POC) technologies has increased during the past decade. Continuous monitoring of patient health status can be achieved through wearable sensors which can be incorporated into clothing and other wearables. While electronic textiles that monitor physical parameters (heart rate, blood pressure, etc.) are increasingly commonplace, smart textiles capable of monitoring chemical biomarkers are much less common. In this work, a conductive plasmonic electrochemical sensor was developed from a cotton blend fabric modified with silver nanoparticles and conductive inks. Para-aminothiophenol (pATP) was used as an initial probe molecule to evaluate the performance of the fabric-based electrode for electrochemical surface-enhanced Raman spectroscopic (EC-SERS) measurements. Further investigation was then carried out to detect levofloxacin, a commonly prescribed antibiotic, in both 0.1 M NaF and synthetic urine as supporting electrolyte. It was found that the fabric-based electrode provided excellent EC-SERS signals, comparable to commercial screen-printed electrodes, allowing for rapid detection of levofloxacin at clinically relevant concentrations. To the best of our knowledge, this is the first time a fabric-based electrode has been reported for EC-SERS investigations, highlighting a promising platform for wearable point-of-care sensors.
Surface enhanced Raman scattering (SERS) is largely used as a transduction method for analytes detection in liquid and vapor phase. In particular, SERS effect was promoted by a plethora of different metal and semiconducting nanoparticles (NPs) and silver and gold nanoparticles appear particularly suitable for this application. Nevertheless, silver nanoparticles intrinsic propensity to aggregate in large clusters reduces the possibility to use naked nanoparticles in SERS applications, for this reason they are usually functionalized with organic molecules. This approach inhibits the aggregation process but, on the other hand, reduces the surficial area of the NPs able to interact with the analyte molecules. In the present work, we propose a simple method to obtain surficial anisotropic Janus silver nanoparticles: octadecylamine was used to stabilize the nanoparticles and to promote the deposition of the silver nanoparticles on a solid substrate. The AgNPs/octadecylamine nanostructures showed the typical “hairy” Janus morphology and a strong SERS effect was observed when two biogenic amines, i. e. 2-phenylethylamine and tyramine, were fluxed on the solid film. SERS phenomenon was studied as a function both of the chemical structure of the fluxed amine and of the distance between the aromatic moiety and the nanoparticle allowing to propose the AgNPs/octadecylamine Janus nanoparticles as an active layer for the detection of phenylethylamine and tyramine in picomolar concentration.
Most individuals adjust their caffeine intake according to the objective and subjective effects induced by the methylxanthine. However, to reach the desired effects, the quantity of caffeine consumed varies largely among individuals. It has been known for decades that the metabolism, clearance, and pharmacokinetics of caffeine is affected by many factors such as age, sex and hormones, liver disease, obesity, smoking, and diet. Caffeine also interacts with many medications. All these factors will be reviewed in the present document and discussed in light of the most recent data concerning the genetic variability affecting caffeine levels and effects at the pharmacokinetic and pharmacodynamic levels that both critically drive the level of caffeine consumption. The pharmacokinetics of caffeine are highly variable among individuals due to a polymorphism at the level of the CYP1A2 isoform of cytochrome P450, which metabolizes 95% of the caffeine ingested. Moreover there is a polymorphism at the level of another critical enzyme,N-acetyltransferase 2. At the pharmacodynamic level, there are several polymorphisms at the main brain target of caffeine, the adenosine A2A receptor or ADORA2. Genetic studies, including genome-wide association studies, identified several loci critically involved in caffeine consumption and its consequences on sleep, anxiety, and potentially in neurodegenerative and psychiatric diseases. We start reaching a better picture on how a multiplicity of biologic mechanisms seems to drive the levels of caffeine consumption, although much more knowledge is still required to understand caffeine consumption and effects on body functions.
Chromatographic methods have become popular in clinical analysis in both routine and research laboratories. The purpose of this review article is to provide an overview of the current state of chromatographic methods, i.e., high-performance liquid chromatography (HPLC), gas chromatography (GC), and supercritical fluid chromatography (SFC), in clinical analysis. The aspects related to method sensitivity, selectivity, analysis time, and throughput have been discussed in detail. Adequate solutions to improve these features have also been presented. HPLC is the most widely used method among the chromatographic methods, whereas GC is dedicated to several specific applications, and SFC is used only marginally certainly due to its only recent comeback to the analytical scene. Based on the literature search, the application fields in clinical analysis are divided into the following groups: drugs, hormones, drugs of abuse, metabolomics, lipidomics, volatile organic compounds, biomarkers and endogenous compounds, proteomics, multi-analyte approches, and others. The important features of these applications have been emphasized.
Surface-enhanced Raman spectroscopy (SERS) has been widely used in a variety of biomedical, analytical, forensic and environmental investigations due to its chemical specificity, label-free nature combined with high sensitivity. Here, we report a simple method for the fabrication of reproducible and reliable, well-defined, stable SERS substrates with uniform and giant Raman enhancement suitable for routine trace chemical analysis and detection of biological compounds in complex biological fluids. We prepared porous silicone (PS) surface by a galvanostatic anodic etch of crystalline silicon wafers. The electrochemical process generates a specific layer of PS: the thickness and porosity of a given layer is controlled by the current density, the duration of the etch cycle, and the composition of the etchant solution. These substrates presented high sensitivity to p-mercaptobenzoic acid (p-MBA) at a low concentration of 10− 6 M and the enhancement factor of over 10⁸ was achieved. Such high enhancement is attributed to semiconducting silicon-induced and stabilized hot spots. The uniform distribution of SERS–active ‘hot-spots’ on the Au/Si surface results in high reproducibility towards detecting p-MBA at 40 different, randomly selected positions on a single substrate (RSD = 6.7%) and on twenty different SERS substrates prepared under identical conditions (RSD = 8%). Designed substrates allow the ultrahigh sensitive and specific detection of human such biofluids as blood, urine and cerebrospinal fluid (CSF) in a reliable, label-free, and reproducible manner. The SERS spectra of these fluids are rich in patient-specific information and can be useful in many analytical and biomedical applications. We have shown that our developed SERS substrates allow the nanomolar detection of neopterin (bacterial infections' marker) in cerebrospinal fluid samples. In order to test the performance of our SERS method in term of low detection limit (LOD), the calibration curve i.e. plot of SERS intensity of the marker band at 695 cm− 1 versus the concentration of neopterin in CSF was constructed and used to calculate the neopterin concentration in clinical samples. The level of neopterin was significantly higher in CSF samples infected by Neisseria meningitidis, (54 nmol/L), compared to normal (control) group, (4.3 nmol/L). The high sensitivity, selectivity and stability of obtained SERS-active substrates combined with simple, low-cost, and easy method of producing offer a promising tool for SERS-based analysis in clinical trials.
Aim:
A central task for the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) is to produce an annual report of the latest data available on drug demand and drug supply in Europe. This paper is intended to facilitate a better understanding of, and easier access to, the main quantitative European level data sets available in 2015.
Methods:
The European reporting system formally covers all 28 European Union (EU) Member States, Norway and Turkey and incorporates multiple indicators alongside an early warning system (EWS) on uncontrolled new psychoactive substances (NPS). While epidemiological information is based largely on registries, surveys and other routine data reported annually, the EWS collects case-based data on an ongoing basis. The 2015 reporting exercise is centred primarily on a set of standardized reporting tools.
Results:
The most recent data provided by European countries are presented, including data on drug use, drug-related morbidity and mortality, treatment demand, drug markets and new psychoactive substances, with data tables provided and methodological information. A number of key results are highlighted for illustrative purposes. Drug prevalence estimates from national surveys since 2012 (last year prevalence of use among the 15-34 age band) range from 0.4% in Turkey to 22.1% in France for cannabis, from 0.2% in Greece and Romania to 4.2% in the United Kingdom for cocaine, from 0.1% in Italy and Turkey to 3% in the Czech Republic and the United Kingdom for ecstasy, and from 0.1% or less in Romania, Italy and Portugal to 2.5% in Estonia for amphetamine. Declining trends in new HIV detections among people who inject drugs are illustrated, in addition to presentation of a breakdown of NPS reported to the EU early warning system, which have risen exponentially from fewer than 20 a year between 2005 and 2008, to 101 reported in 2014.
Conclusions:
Structured information is now available on patterns and trends in drug consumption in Europe, which permits triangulation of data from different sources and consideration of methodological limitations. Opioid drugs continue to place a burden on the drug treatment system, although both new heroin entrants and injecting show declines. More than 450 new psychoactive substances are now monitored by the European early warning system with 31 new synthetic cathinones and 30 new synthetic cannabinoid receptor agonists notified in 2014.
Uric acid is a potential important biomarker in urine and serum samples for early diagnosis of preeclampsia, a life-threatening hypertensive disorder that occurs during pregnancy. Preeclampsia is a leading cause of maternal death, especial-ly in developing nation settings. Quantitative detection of uric acid for rapid and routine diagnosis of early preeclampsia using electrochemical-surface enhanced Raman spectroscopy (EC-SERS) is presented herein. A uniform EC-SERS active Au/Ag substrate was developed by depositing nearly monodisperse gold and silver nanoparticles on the carbon working elec-trode surface of screen printed electrodes. The multilayered Au/Ag substrates were characterized by electron microscopy and used for quantitative detection of uric acid in 0.1 M NaF and synthetic urine at clinically relevant concentrations. These results showed a linear relationship between the EC-SERS signal intensity and the uric acid concentration. Relative errors calculated for selected concentrations were all within the CLIA criterion for uric acid analysis (±17%). It is believed that rou-tine and early diagnosis of disease could be possible through such quantitative detection of biomarkers in patient samples using this EC-SERS method.
This study determines the mean concentrations of free amino acids in stimulated and unstimulated whole saliva in healthy young adults. Standardised salivary amino acids as a substitute for their counterpart in blood, searched for the source of free amino acids in saliva, the probable correlation between particular amino acids with caries experience. Stimulated and unstimulated whole saliva were collected by the draining method in 31 dental students. Saliva was purified, and amino acids were separated by high-performance liquid chromatography. DMFT scores were recorded, and the relation of amino acids to caries experience was explored by generalised linear model. Almost all amino acids had higher concentration in unstimulated whole saliva than in stimulated saliva. The normal range of amino acids (95% CI) and their natural logarithm were defined. There was a significant relationship between caries experience and threonine (P < 0·008), citrulline (P < 0·023) and ornithine (P < 0·001) as a detrimental factor, whereas serin (P < 0·026), glutamine (P < 0·015) and phenylalanine (P < 0·014) had an inhibiting effect on caries. However, in comparison, salivary flow rate (P < 0·013) was a more preventive factor than amino acids. Amino acids in saliva contribute as a marker, instead of their counterpart in blood. Unstimulated saliva had higher concentration of amino acids. Amino acids have different impact on caries and may be one of underlying risk factors for caries experience.
There remains a need for objective and cost-effective approaches capable of diagnosing early-stage disease in point-of-care clinical settings. Given an increasingly ageing population resulting in a rising prevalence of chronic diseases, the need for screening to facilitate the personalising of therapies to prevent or slow down pathology development will increase. Such a tool needs to be robust but simple enough to be implemented into clinical practice. There is interest in extracting biomarkers from biofluids (e.g., plasma or serum); techniques based on vibrational spectroscopy provide an option. Sample preparation is minimal, techniques involved are relatively low-cost, and data frameworks are available. This review explores the evidence supporting the applicability of vibrational spectroscopy to generate spectral biomarkers of disease in biofluids. We extend the inter-disciplinary nature of this approach to hypothesise a microfluidic platform that could allow such measurements. With an appropriate lightsource, such engineering could revolutionize screening in the 21(st) century. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).
Several negatively charged dyes were investigated for their possible adsorption on the surface of silver and gold colloidal particles. Those dyes that were found to adsorb on the particles were then checked for surface enhancement of Raman scattering. Highly efficient surface-enhanced Raman scattering (SERS) was observed from a carbocyanine dye in both sols. Excitation-dependence studies as well as adsorption studies confirm the SERS nature of the Raman spectra obtained. The dye is probably aggregated on adsorption and is probably attached through the naphthalene side moiety to the surface. Less efficient SERS was also observed for copper phthalocyanine.
The surface enhanced Raman scattering (SERS) of caffeine on borohydride-reduced silver colloids system under different aqueous solution environment has been studied in this paper. The relative intensity of SERS of caffeine significantly varies with different concentrations of sodium chloride and silver particles. However, at too high or too low concentration of sodium chloride and silver particle, the enhancement of SERS spectra is not evident. The SERS spectra of caffeine suggest that the contribution of the charge transfer mechanism to SERS may be dominant. The chloride ions can significantly enhance the efficiency of SERS, while the enhancement is selective, as the efficiency in charge transfer enhancement is higher than in electromagnetic enhancement. Therefore, it can be concluded that the active site of chloride ion locates on the bond between the caffeine and the silver surface. In addition, the SERS spectra of caffeine on borohydride-reduced and citrate-reduced silver colloids are different, which may be due to different states caffeine adsorbed on silver surface under different silver colloids.
To investigate the utility of metrics of CYP1A2 activity using caffeine as a probe, and saliva and plasma sampling with or without a 24-h caffeine abstinence.
This was a cross-over pharmacokinetic study in 30 healthy male subjects who received a single oral 100mg caffeine dose after 24-h caffeine abstinence or after maintaining their regular caffeine intake (no caffeine abstinence). Serial blood and saliva samples were collected simultaneously over 24h. Caffeine and paraxanthine concentrations were measured using a validated HPLC assay.
There was a strong correlation between the paraxanthine/caffeine AUC(0-24) ratio (reference metric) and the paraxanthine/caffeine concentration (C(t) ) ratio at 4h (C(4) ) in both saliva and plasma (r≥0.75). The paraxanthine/caffeine AUC(0-24) ratio in plasma and saliva did not differ between the 24-h caffeine abstinence and the no abstinence period (P>0.05). The optimal paraxanthine/caffeine C(t) that correlated with the plasma paraxanthine/caffeine AUC(0-24) ratio in the 24-h abstinence period was 2 and 4h (r=0.88) in plasma, and 4 and 6h in saliva (r=0.70), while it was the saliva 4h time-point in the no abstinence period (r=0.78).
The saliva paraxanthine/caffeine concentration ratio at 4h was a suitable metric to assess CYP1A2 activity after oral administration of caffeine without the need for 24-h caffeine abstinence.
Surface chemistry can become pronounced in determining the optical properties of colloidal metal nanoparticles as the nanoparticles become so small (diameters <20 nm) that the surface atoms, which can undergo chemical interactions with the environment, represent a significant fraction of the total number of atoms although this effect is often ignored. For instance, formation of chemical bonds between surface atoms of small metal nanoparticles and capping molecules that help stabilize the nanoparticles can reduce the density of conduction band electrons in the surface layer of metal atoms. This reduced electron density consequently influences the frequency-dependent dielectric constant of the metal atoms in the surface layer and, for sufficiently high surface to volume ratios, the overall surface plasmon resonance (SPR) absorption spectrum. The important role of surface chemistry is highlighted here by carefully analyzing the classical Mie theory and a multi-layer model is presented to produce more accurate predictions by considering the chemically reduced density of conduction band electrons in the outer shell of metal atoms in nanoparticles. Calculated absorption spectra of small Ag nanoparticles quantitatively agree with the experimental results for our monodispersed Ag nanoparticles synthesized via a well-defined chemical reduction process, revealing an exceptional size-dependence of absorption peak positions: the peaks first blue-shift followed by a turnover and a dramatic red-shift as the particle size decreases. A comprehensive understanding of the relationship between surface chemistry and optical properties is beneficial to exploit new applications of small colloidal metal nanoparticles, such as colorimetric sensing, electrochromic devices, and surface enhanced spectroscopies.
The pharmacokinetics of caffeine (CA), paraxanthine (PX), theobromine (TB) and theophylline (TP) were studied in six healthy male volunteers after oral administration of each compound on separate occasions. The total plasma clearances of CA and PX were similar in value (2.07 and 2.20 ml min-1 kg-1, respectively) as were those for TP and TB (0.93 and 1.20 ml min-1 kg-1, respectively). The unbound plasma clearances of CA and PX were also similar in magnitude (3.11 and 4.14 ml min-1 kg-1, respectively) as were those of TP and TB (1.61 and 1.39 ml min-1 kg-1, respectively). The half-lives of TP and TB (6.2 and 7.2 h, respectively) were significantly longer than those of CA and PX (4.1 and 3.1 h, respectively). The volume of distribution at steady state of TP (0.44 l kg-1) was lower than that of the other methylxanthines (0.63-0.72 l kg-1). The unbound volume of distribution of TP (0.77 l kg-1) was however the same as that of TB (0.79 l kg-1) whereas the unbound volume of distribution of PX (1.18 l kg-1) was similar to that of CA (1.06 l kg-1).
The surface enhanced Raman spectroscopy (SERS) spectrum of caffeine is recorded on a silver colloid at different pH values. It is discussed on the basis of the SERS "surface selection rules" in order to characterize its vibrational behavior on such a biological artificial model. To improve the previous assignments in the Raman spectrum and for a reliable, detailed analysis of SERS spectra, density functional theory calculations (structural parameters, harmonic vibrational wavenumbers, total electron density, and natural population analysis of the molecule) are performed for the anhydrous form of caffeine and the results are discussed. The predicted geometry and vibrational Raman spectra are in good agreement with the experimental data. The flat orientation of the mainly chemisorbed caffeine attached through the pi electrons and the lone pair of nonmethylated N atoms of the imidazole ring are proposed to occur at neutral and basic pH values. At acid pH values caffeine is probably adsorbed on the Ag surface through one or both oxygen atoms, more probably through the O atom of the conjugated carbonyl group with an end-on orientation. However, the changes in the overall SERS spectral pattern seem to indicate the electromagnetic mechanism as being the dominant one.
Surface enhanced Raman spectroscopy
- Schlucker