Article

Biomolecular Stiffness Detection Based on Positive Frequency Shift of CMOS Compatible Gigahertz Solidly Mounted Resonators

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Abstract

In this work, gigahertz solidly mounted resonators (SMRs) (2.5 GHz) were designed and fabricated to construct a novel particle-resonator system to achieve the biomolecular stiffness sensing in real time. The positive frequency shift of the system was used to estimate the stiffness of biomolecules connecting between the SMR and attached particles. The working principle was revealed by the mathematical analysis of the general block-spring model of the system. Further interpretations about the mechanism of such elastic interaction from the perspective of acoustic resonant modes of SMRs were given by finite element method. Biotin-streptavidin, antibody and antigen binding system were used as model molecular linkers to study the frequency shift varied with different particle diameters and particle densities. Different linker stiffness was realized by adjusting the concentrations of antigens connected with particles which form specific binding with antibodies immobilized on the SMR. The results fairly agree with the simulation results demonstrating the proposed particle-resonator system as an effective method to realize the real-time biomolecular stiffness detection.

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... Among the various detection technologies, mass-sensitive sensors based on piezoelectric resonators have attracted considerable attention for biomolecule detection during the last few decades due to their high selectivity and sensitivity. 10,11 In generally, these piezoelectric resonator sensors can be divided into two categories (determined by the transmission paths of acoustic wave resonance) surface acoustic wave (SAW) and bulk acoustic wave (BAW) sensors. However, the SAW sensors cannot achieve a higher sensitivity due to the restriction on dimension of the delay line for the interdigital transducer (IDT) and the resonant frequency (from 30 MHz to 1 GHz). ...
... However, the SAW sensors cannot achieve a higher sensitivity due to the restriction on dimension of the delay line for the interdigital transducer (IDT) and the resonant frequency (from 30 MHz to 1 GHz). 12,13 In addition, the quartz crystal microbalance (QCM) employed in BAW sensors has a mass detection limit in the order of nanograms determined from their low operation frequency (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) due to the bulk quartz substrate thickness. Thus BAW sensors do not have adequate sensitivity for the detection of small molecules in low concentrations. ...
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During the past decade, physical techniques such as optical tweezers and atomic force microscopy were used to study the mechanical properties of DNA at the single-molecule level. Knowledge of DNA's stretching and twisting properties now permits these single-molecule techniques to be used in the study of biological processes such as DNA replication and transcription.
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We report biophysical experiments performed on the bacterium Listeria monocytogenes, a model system to study actin-based motility. Using optical tweezers and electrophoresis experiments, we find that the bacterium is firmly attached to its tail, and we demonstrate that the tail responds as an elastic gel when deformed. We have measured its elastic modulus at a value of 10(3)-10(4) Pa, which is 10 times higher than the rigidity of the eukaryotic cytoplasm. These results demonstrate that the bacterium and its tail form a very robust system, consistent with the steadyness of the motion observed in vivo. We propose an elastic model for the propulsion mechanism which takes into account the connection and thus the interaction between the actin filaments. It provides a generic description of the various aspects of actin-tail based movements.
Article
Coiled-coils occur in a variety of proteins involved in mechanical and structural tasks in the cell. Their mechanical properties are important in various contexts ranging from hair elasticity to synaptic fusion. Beyond their importance in biology, coiled-coils have also attracted interest as programmable protein sequences for the design of novel hydrogels and materials. We have studied the elastic properties of the myosin coiled-coil at the single molecule level. The coiled-coil undergoes a massive structural transition at forces between 20 and 25 pN where the coil extends to about 2.5 times its original length. Unlike all other proteins investigated mechanically so far, this transition is reversible on a timescale of less than a second, making the coiled-coil a truly elastic protein.
Article
Atomic force microscopy allows three-dimensional imaging and measurements of unstained and uncoated biological samples in air or fluid. Using this technology it offers resolution on the nanometer scale and detection of temporal changes in the mechanical properties, i.e. surface stiffness or elasticity in live cells and membranes. Various biological processes including ligand-receptor interactions, reorganization, and restructuring of the cytoskeleton associated with cell motility that are governed by intermolecular forces and their mode of detection will be discussed.
Article
The adhesion of lactic acid bacteria to the intestinal epithelium is one of the most important factors determining probiotic ability of a bacterial strain. Studying bacterial adhesion requires knowledge of the structure and properties of the bacterial surface, which can be studied by atomic force microscopy under native conditions. The observation of the surface topography of bacteria from the species Lactobacillus crispatus, L. helveticus and L. johnsonii shows major differences between bacteria having a crystalline-like protein layer as part of the cell wall and those without such layers. Force volume images calculated into elasticity and adhesion force maps of different bacterial strains show that L. crispatus and L. helveticus have a surface with a homogeneous stiffness with no adhesion events. This is most likely caused by the S-layer, which completely covers the surface of the bacteria. We infer that the absence of adhesion peaks is caused by the semi-crystalline character of such protein layers, in agreement with the results obtained from electron microscopy. Analysis of a number of L. johnsonii strains shows that these bacteria have surface properties which strongly differ from the L. crispatus and L. helveticus strains. For L. johnsonii DMS20533 and L. johnsonii ATCC33200 high adhesion forces are observed, which can be related to a surface rich in polysaccharides. L. johnsonii ATCC332 has lower adhesion forces compared to the other two and, furthermore, the surface topography shows depressions. We suppose that this strain has a surface pattern consisting of crystalline-like proteins alternating with polysaccharide-rich domains. The wide variety in surface properties of lactobacilli could well have wide-ranging implications for food processing and for health benefits.
Article
A novel integrated bio-sensor technology based on thin-film bulk acoustic wave resonators on silicon is presented and the feasibility of detecting DNA and protein molecules proofed. The detection principle of these sensors is label-free and relies on a resonance frequency shift caused by mass loading of an acoustic resonator, a principle very well known from quartz crystal micro balances. Integrated ZnO bulk acoustic wave resonators with resonance frequencies around 2 GHz have been fabricated, employing an acoustic mirror for isolation from the silicon substrate. DNA oligos have been thiol-coupled to the gold electrode by on-wafer dispensing. In a further step, samples have either been hybridised or alternatively a protein has been coupled to the receptor. The measurement results show the new bio-sensor being capable of both, detecting proteins as well as the DNA hybridisation without using a label. Due to the substantially higher oscillation frequency, these sensors already show much higher sensitivity and resolution comparable to quartz crystal micro balances. The potential for these sensors and sensors arrays as well as technological challenges will be discussed in detail.
Article
We show how the water content (and effective density) of thin adsorbed films composed of biomolecules can be determined using combined quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) analysis. In particular, these techniques, combined with theoretical treatment using a Voigt-based viscoelastic model, were applied to analyze the state of surface immobilized single stranded biotin-modified probe DNA (b-DNA) coupled via streptavidin to a biotin-doped supported phospholipid bilayer (b-SPB)). From a proper analysis, it is demonstrated how changes in effective thickness, delta(f), and the viscoelastic components (shear viscosity, eta(f), and shear elasticity, mu(f))) can be obtained during both DNA immobilization and hybridization with single stranded fully complementary target DNA. In particular, it is demonstrated how this type of analysis can be used to control the state of streptavidin arrangement for improved measurements of DNA hybridization kinetics. The latter is demonstrated by identifying a surface-coverage dependent viscoelastic behavior of immobilized b-DNA, which is shown to influence the hybridization efficiency.
Article
For a thin viscoelastic film deposited on a quartz crystal microbalance in a liquid environment, the change in dissipation induced by the presence of a film is proportional to the film's elastic compliance, Jf'. This surprising result is a consequence of the fact that the film is "clamped" by a viscous fluid.
Article
Particulate interactions are dominated by aspects such as surface topography, exposed chemical moieties, environmental conditions, and thermodynamic properties such as surface free energy (gamma). The absolute value and relative magnitude of surface energies of a drug and excipients within a formulation can significantly influence manufacture, processing, and use. This study utilizes and compares the potentially complementary analytical techniques of atomic force microscopy (AFM) and inverse gas chromatography (IGC) in the quantitative determination of the surface energy of drug (budesonide) particles (micronized and unmilled) relevant to inhaled delivery. In addition, the study investigates with AFM another important parameter in determining material interactions, the local mechanical properties of the drug. AFM was used to acquire force of adhesion (Fadh) and related work of adhesion (WA) and surface energy values between individual mironized drug particles and also model substrates (graphite and mica). In addition, AFM probes were used to interrogate the surface energy of unmilled drug particles. Measurement with AFM probes also yielded localized measurements of Young's modulus for the unmilled drug. IGC was also used to probe the surface characteristics of the bulk drug material. The average values for surface energies acquired from budesonide micronized particle interactions with graphite, mica, and drug particles of the same substance were found to range from 35 to 175, 5 to 40, and 10 to 32 mJ m(-2), respectively. The unmilled material displayed a range of values of 39-88 mJ m(-2) with an average of 60 mJ m(-2). The IGC result for the surface energy of the micronized material was 68.47 +/- 1.60 mJ m(-2). The variability in surface energy from AFM, a feature particularly apparent for the micronized material was attributed to two factors, intrinsic material variations within a single particle and assumptions present within the contact mechanics model used. Here we provide a detailed description of these factors to go some way to rationalize the results. The Young's modulus of the unmilled drug was determined to be approximately 10 GPa. The range of determined surface energies between the AFM measurement on graphite, mica, and the drug is proposed to reflect the different chemistries displayed by the drug at the single particle level. The maximum values of these ranges can be related to the sites most likely to be involved in adhesion. AFM and IGC yield surface energy estimates in approximate agreement, but clearly are interrogating surfaces in different fashions. This raises questions as to the nature of the measurement being made by these approaches and to the most appropriate time to use these methods in terms of a direct relation to formulation design, manufacture, and drug delivery. Finally, we demonstrate a novel method for assessing the Young's modulus of a drug from a single particle.
Article
The hydration-dehydration process of an adsorbed human serum albumin film has been studied using atomic force microscopy (AFM) and a quartz crystal microbalance (QCM). All measurements were performed with identically prepared protein films deposited on highly hydrophilic substrates. Both techniques are shown to be suitable for following in situ the kinetics of protein hydration, and for providing quantitative values of the adsorbed adlayer mass. The results obtained by the two methods have been compared and combined to study changes of physical properties of the films in terms of viscosity, shear, Young's modulus, density and film thickness. These properties were found to be reversible during hydration-dehydration cycles.