Publications (10)25.66 Total impact
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Article: Electrochemical impedance spectroscopic technique with a functionalized microwire sensor for rapid detection of foodborne pathogens.
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ABSTRACT: In this study, a label-free biosensor based on electrochemical impedance measurement followed by dielectrophoretic force and antibody-antigen interaction was developed for detection and quantification of foodborne pathogenic bacteria. In our previous work, gold-tungsten wires (25μm in diameter) were functionalized by coating with polyethyleneimine-streptavidin-anti-Escherichia coli antibodies to improve sensing specificity, and fluorescence intensity measurement was employed to quantify bacteria captured by the sensor. The focus of this research is to evaluate the performance of the developed biosensor by monitoring the changes of electron-transfer resistance (ΔR(et)) of the microwire after the bioaffinity reaction between bacterial cells and antibodies on its surface as an alternative quantification technique to fluorescence microscopy. Electrochemical impedance spectroscopy (EIS) has been used to detect and validate the resistance changes in a conventional three-electrode system in which [Fe(CN)(6)(3-)]/[Fe(CN)(6)(4-)] served as the redox probe. The impedance data demonstrated a linear relationship between the increments of ΔR(et) and the logarithmic concentrations of E. coli suspension in the range of 10(3)-10(8)CFU/mL. In addition, there were little changes of ΔR(et) when the sensor worked with Salmonella, which clearly evidenced the sensing specificity to E. coli. EIS was proven to be an ideal alternative to fluorescence microscopy for enumeration of captured cells.Biosensors & bioelectronics 10/2012; 42C:492-495. · 5.43 Impact Factor -
Article: Evaluation of a microwire sensor functionalized to detect Escherichia coli bacterial cells.
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ABSTRACT: A functionalized microwire sensor based on dielectrophoresis (DEP) and antigen-antibody reaction was initially developed for sensitive and selective detection of E. coli O157:H7. The dynamics of gold-tungsten microwires were manipulated using an automated X-Y-Z stage and the sensing process included antibody immobilization and bacterial detection, and cell quantification. Antibodies were first immobilized on surface of the microwire to improve sensing specificity, and then coupled with DEP for capture of E. coli cells in a mixture of E. coli cells and non-conductive polystyrene beads. Afterward, fluorescein-conjugated secondary antibodies were applied to the wire for quantification of captured bacteria. Field Emission Scanning Electron Microscope (FESEM) figures and fluorescence intensities of bacteria on the wire validated the sensing mechanism. The entire immobilization and detection procedure could be completed within 30 min with simple operations. Performance of the microwire sensor was not significantly affected when conducted in orange juice. In addition, the detection limit of this sensor was about 5 bacterial cells per microwire in 1000 CFU/mL bacterial suspensions when the electric field generated at 3 MHz and 20 peak to peak voltage (V(pp)), and only targeted E. coli cells were concentrated and captured.Biosensors & bioelectronics 04/2012; 36(1):257-61. · 5.43 Impact Factor -
Article: A microwire sensor for rapid detection of Escherichia coli K-12 in fresh produce
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ABSTRACT: A rapid immunofluorescence method for foodborne pathogens in food systems using microwire sensor coupled with high frequency alternating current was developed. The method was intended to enrich and quantify E. coli cells internalized in baby spinach leaves. The targeted bacterial cells in the sample solution were captured on microwires in a diameter of 25μm, and were bound to fluorescein isothiocyanate (FITC) labeled polyclonal E. coli antibodies. Fluorescent images of the FITC antibodies were obtained using a fluorescence microscope equipped with a charge-coupled-device (CCD) camera, and the fluorescent intensity (FI) was quantified through image processing. The capture of E. coli K-12 in PBS buffer was optimized when the electric field was generated at the frequency of 3MHz and 20Vpp with bacterial concentration of 107CFU/mL. The detection limit of our sensing device was determined to be 103CFU/mL. Field emission scanning electron microscopy (FESEM) was used to validate and visualize E. coli cells captured on the tip surface. The sensitivity and specificity of the developed sensor has been successfully validated by testing E. coli internalized in baby spinach leaves. The immunofluorescence detection has been completed within 15min. Moreover, it was found that the enrichment process of E. coli cells using the dielectrophoretic force was rarely affected by food particles, which proved the sensing selectivity. The developed sensor is expected to meet the steady demand for a simple, rapid, highly sensitive detection approach to quantify the targeted microbes in food systems.Innovative Food Science & Emerging Technologies - INNOV FOOD SCI EMERG TECHNOL. 01/2011; 12(4):617-622. -
Article: Simple quantitative analysis of Escherichia coli K-12 internalized in baby spinach using Fourier Transform Infrared spectroscopy.
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ABSTRACT: Bacterial contamination continues to be a serious concern for food safety. Although washing fresh produce helps in reducing pathogen levels, pathogen internalization often limits the effectiveness of washing. When pathogens internalize in leafy vegetables, the method of identification and quantitative measurement would be called into question. This study was aimed to use Fourier Transform Infrared (FTIR) spectroscopy integrated with an attenuated total reflectance kit for quantification of Escherichia coli K-12 internalized in baby spinach. The bacteria were inoculated into vascular and intracellar tissues of spinach leaves by syringe injection and the distribution of internalized E. coli K-12 cells was confirmed under scanning electron microscopy (SEM). FTIR measurement following the preparation of bacterial suspension from spinach leaves with high speed pulverizing enabled to detect the absorbance peaks in the amide II region between 1590 and 1490 cm⁻¹ as a fingerprint for the microbes. It was found that the estimated concentrations of E. coli K-12 agreed well with the concentrations determined by plate counting with R² values of 0.98 and 0.97 in peptone water and spinach extracts, respectively. The results demonstrated that FTIR can identify and quantify E. coli K-12 in baby spinach extracts at a limit of detection of approximately 100 CFU/mL in 5 min. The developed method is expected to be suitable for the analysis of pathogenic E. coli strains and other bacterial species in fresh vegetables.International journal of food microbiology 10/2010; 144(1):147-51. · 3.01 Impact Factor -
Article: Rapid analysis of glucose, fructose, sucrose, and maltose in honeys from different geographic regions using fourier transform infrared spectroscopy and multivariate analysis.
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ABSTRACT: Quantitative analysis of glucose, fructose, sucrose, and maltose in different geographic origin honey samples in the world using the Fourier transform infrared (FTIR) spectroscopy and chemometrics such as partial least squares (PLS) and principal component regression was studied. The calibration series consisted of 45 standard mixtures, which were made up of glucose, fructose, sucrose, and maltose. There were distinct peak variations of all sugar mixtures in the spectral "fingerprint" region between 1500 and 800 cm(-1). The calibration model was successfully validated using 7 synthetic blend sets of sugars. The PLS 2nd-derivative model showed the highest degree of prediction accuracy with a highest R(2) value of 0.999. Along with the canonical variate analysis, the calibration model further validated by high-performance liquid chromatography measurements for commercial honey samples demonstrates that FTIR can qualitatively and quantitatively determine the presence of glucose, fructose, sucrose, and maltose in multiple regional honey samples.Journal of Food Science 03/2010; 75(2):C208-14. · 1.66 Impact Factor -
Article: Residues of polybrominated diphenyl ethers in honeys from different geographic regions.
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ABSTRACT: Polybrominated diphenyl ethers (PBDEs) are a class of widely used flame-retardants. Fifty honey samples labeled as being from different countries and regions were analyzed for 27 PBDE congeners. The concentrations of the 26 PBDEs, excluding BDE-209, ranged from 300 to 10,550 pg/g while the concentrations of BDE-209 ranged from nondetected to 9,260 pg/g. The honey samples labeled as originating in developed countries generally displayed higher concentrations of the total 27 PBDEs than those labeled as being from developing countries. Concentrations of 26 PBDEs ranged from 2,720 to 10,550 pg/g in honeys originating in developed countries and ranged from 1,030 to 3,470 pg/g in those from developing countries. BDE-209 was a dominant PBDE congener in all honey samples, on average accounting for 16% and 65% of the total 27 PBDEs in honeys from developed and developing countries, respectively. Honeys originating in developing countries, however, showed much higher BDE-209 levels and higher ratios of BDE-209 relative to the other PBDE congeners. In addition, some highly brominated PBDE congeners such as BDE-196, -197, -206, and -207 showed elevated concentrations in honeys from developing countries. The findings were in agreement with the long, heavy historical uses of PBDE products in developed countries and the current, heavy uses of BDE-209 in developing countries. When BDE-209 was fortified in honey and incubated in the dark for four weeks at 25 or 60 degrees C, BDE-153, -183, -206, and -207 were detected as debromination products of BDE-209. Less brominated congeners in honeys may primarily come from the environment. Debromination of BDE-209 is also a source of less brominated congeners in honeys. The detection of PBDEs in honeys suggests that human exposure to PBDEs occurs as a result of honey consumption.Journal of Agricultural and Food Chemistry 02/2010; 58(6):3495-501. · 2.82 Impact Factor -
Article: Rapid determination of the geographical origin of honey based on protein fingerprinting and barcoding using MALDI TOF MS.
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ABSTRACT: The authentication of foods is an important aspect of quality control and food safety. Honey is one of the most natural and most popular foods in the world. A fast and reliable method to determine the geographical origin of honey was developed based on fingerprinting and barcoding of proteins in honey by using matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI TOF MS) and MALDI Biotyper 1.1 software, respectively. The protein mass spectra of 16 honey samples of known Hawaii origin were obtained and peak information was extracted to generate protein fingerprints. This information was transformed into a database library of spectral barcodes that were used for differentiation of the geographical origin of honeys based on pattern matching. The differentiation ability of the database library of barcodes was validated by comparing the results of replicate assays of 5 of the 16 honey samples of known Hawaii origin obtained directly from the producers. Validation results showed that the protein fingerprints of honeys have better comparability with those honeys in the library known to be from the same region than with those of honey samples from other regions. The protein fingerprints were used to differentiate the geographical origins of commercially purchased honey samples with labels indicating that they were produced in different countries and various states of the USA, including Hawaii. The results showed that the MALDI TOF MS Biotyper system can be a rapid, simple and practical method for determining the geographical origin of honeys sold in commerce.Journal of Agricultural and Food Chemistry 11/2009; 57(21):10081-8. · 2.82 Impact Factor -
Article: Fourier transform infrared spectroscopy for Kona coffee authentication.
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ABSTRACT: Kona coffee, the variety of "Kona typica" grown in the north and south districts of Kona-Island, carries a unique stamp of the region of Big Island of Hawaii, U.S.A. The excellent quality of Kona coffee makes it among the best coffee products in the world. Fourier transform infrared (FTIR) spectroscopy integrated with an attenuated total reflectance (ATR) accessory and multivariate analysis was used for qualitative and quantitative analysis of ground and brewed Kona coffee and blends made with Kona coffee. The calibration set of Kona coffee consisted of 10 different blends of Kona-grown original coffee mixture from 14 different farms in Hawaii and a non-Kona-grown original coffee mixture from 3 different sampling sites in Hawaii. Derivative transformations (1st and 2nd), mathematical enhancements such as mean centering and variance scaling, multivariate regressions by partial least square (PLS), and principal components regression (PCR) were implemented to develop and enhance the calibration model. The calibration model was successfully validated using 9 synthetic blend sets of 100% Kona coffee mixture and its adulterant, 100% non-Kona coffee mixture. There were distinct peak variations of ground and brewed coffee blends in the spectral "fingerprint" region between 800 and 1900 cm(-1). The PLS-2nd derivative calibration model based on brewed Kona coffee with mean centering data processing showed the highest degree of accuracy with the lowest standard error of calibration value of 0.81 and the highest R(2) value of 0.999. The model was further validated by quantitative analysis of commercial Kona coffee blends. Results demonstrate that FTIR can be a rapid alternative to authenticate Kona coffee, which only needs very quick and simple sample preparations.Journal of Food Science 07/2009; 74(5):C385-91. · 1.66 Impact Factor -
Article: Application of multibounce attenuated total reflectance fourier transform infrared spectroscopy and chemometrics for determination of aspartame in soft drinks.
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ABSTRACT: Aspartame is a low-calorie sweetener commonly used in soft drinks; however, the maximum usage dose is limited by the U.S. Food and Drug Administration. Fourier transform infrared (FTIR) spectroscopy with attenuated total reflectance sampling accessory and partial least-squares regression (PLS) was used for rapid determination of aspartame in soft drinks. On the basis of spectral characterization, the highest R2 value, and lowest PRESS value, the spectral region between 1600 and 1900 cm(-1) was selected for quantitative estimation of aspartame. The potential of FTIR spectroscopy for aspartame quantification was examined and validated by the conventional HPLC method. Using the FTIR method, aspartame contents in four selected carbonated diet soft drinks were found to average from 0.43 to 0.50 mg/mL with prediction errors ranging from 2.4 to 5.7% when compared with HPLC measurements. The developed method also showed a high degree of accuracy because real samples were used for calibration, thus minimizing potential interference errors. The FTIR method developed can be suitably used for routine quality control analysis of aspartame in the beverage-manufacturing sector.Journal of Agricultural and Food Chemistry 03/2008; 56(3):778-83. · 2.82 Impact Factor -
Article: Quantification of trans fatty acid content in French fries of local food service retailers using attenuated total reflection – Fourier transform infrared spectroscopy
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ABSTRACT: The contents of trans fatty acids in French fries served at the local food service retailers in Honolulu were determined by simple Fourier transform infrared (FTIR) spectroscopic technique without the pretreatment of fatty acid extraction. A horizontal attenuated total reflection (ATR) crystal made of zinc selenide (ZnSe) was used to obtain FTIR spectra of French fries with and without fatty acid extraction. Residual oil films obtained by pressing French fries directly on the ATR crystal surface without removal of any solid particles or air bubbles were scanned for the spectral measurement. The calibration set consisted of triolein (C18:1, 9-cis) and trielaidin (C18:1, 9-trans) mixed in varying ratios. All spectral data were averaged and converted into GRAMS format. The peak heights of each spectrum at 966 cm−1 were found to be linearly correlated with the contents of trans fatty acids in the validation set (n = 8, R2 = 0.9835). The developed calibration model was validated by comparing the results obtained from the ATR-FTIR with Mojonnier extraction and gas chromatography–mass spectrometry (GC–MS).Food Chemistry.
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2008–2012
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University of Hawaiʻi at Mānoa
- Department of Molecular Biosciences and Bioengineering
Honolulu, HI, USA
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