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PubMed2005

Functional monolayers for improved resistance to protein adsorption: oligo(ethylene glycol)-modified silicon and diamond surfaces.

The interaction of proteins with semiconductors such as silicon and diamond is of great interest for applications such as electronic biosensing. We have investigated the use of covalently bound oligo(ethylene glycol), EG, monolayers on diamond and silicon to minimize nonspecific protein adsorption. Protein adsorption was monitored by fluorescence scanning as a function of the length of the ethylene glycol chain (EG3 through EG6) and the terminal functional group (methyl- versus hydroxyl-terminated EG3 monolayer). More quantitative measurements were made by eluting adsorbed avidin from the surface and measuring the intensity of fluorescence in the solution. The attachment chemistry of the tri(ethylene glycol) molecules and monolayer orientation was studied by X-ray photoelectron spectroscopy. Improvement in the selectivity of surfaces modified with EG functionality was demonstrated in two model biosensing assays. We find that high-quality EG monolayers are formed on silicon and diamond and that these EG3 monolayers are as effective as EG3 self-assembled monolayers on gold at resisting nonspecific avidin adsorption. These results show promise for use of silicon and diamond materials in many potential applications such as biosensing and medical implants.

Adsorption↗
PubMed1999

[Department of microbiosensing system using micromachine techniques].

This paper reviews devices for Point Of Care (POC) testing, especially focusing on current and future biosensors and biosensing fields. POC testing involves on-site diagnosis such as bedside diagnosis and near-patient testing. Biosensors and biosensing devices are a key technology to measure all clinically important parameters. For many reasons such as historical, simplicity, the high stability and activity of the enzyme required, and large demand from diabetics, only glucose sensors are commercially available. Various biosensors are waiting for commercialization. Not only simple biosensors having a biofunctional membrane on a transducer, but more complicated biosensing systems are fabricated on a microchip. Micro-Total Analysis System (mu TAS) is a research field to fabricate miniaturized sensing devices or systems. In these devices or systems, biochemical reactions for detection can be well controlled by running buffers, even though the consumption of reagents and sample is very small. Microarray chip technology, such as the DNA chip, is now receiving much attention in not only genetic research, but other biochemical research and application fields as well. Detection apparatus for the DNA chip is currently bench-top size. According to recent research, however, the size will be reduced as to a portable-size that is suitable for POC testing. Research and development of POC devices are advanced not alternative methods of conventional laboratory test, but as complement technology with advantages such as mobility, speed, and low-cost.

Biosensing Techniques↗
PubMedDate not supplied

[DNA liquid-crystalline dispersion particles as a basis for sensitive biosensor elements].

The data on the morphology, structural parameters, and abnormal optical properties of particles of cholesteric liquid-crystalline dispersions of double-stranded DNA are reviewed. The general principles of the creation and operation of biosensing units based on particles of these suspensions, including dispersed particles immobilized in hydrogels, are described. Examples demonstrating the analytical potentialities of liquid-crystalline biosensing units are given. A method for constructing "sandwich"-type biosensing units based on the particles of liquid-crystalline dispersion formed from molecules of DNA-polycation complexes is described.

Biosensing Techniques↗
PubMed2002

Magnetic resonance imaging demonstrates improved regional systolic wall motion and thickening and myocardial perfusion of myocardial territories treated by laser myocardial revascularization.

OBJECTIVES: This study was designed to investigate the use of magnetic resonance (MR) functional and perfusion imaging to evaluate laser myocardial revascularization (LMR). BACKGROUND: Most clinical studies of LMR have shown improvements in angina class and exercise capacity, with minimal or absent improvements in myocardial perfusion and function. METHODS: Fifteen patients who underwent percutaneous Biosense-guided holmium:yttrium aluminum garnet LMR to areas of viable but ischemic myocardium were followed clinically and underwent functional and perfusion MRI at baseline, 30 days and 6 months. RESULTS: The mean age was 64 +/- 11 years; four patients were women. The ejection fraction was 47.4 +/- 14.0%. Angina class at baseline was 3.4 +/- 0.6 and improved to 2.5 +/- 1.4 at six months (p = 0.054). Exercise time at baseline was 298 +/- 97 s and increased to 350 +/- 95 s at 30 days and 365 +/- 79 s at six months, p = 0.04. There were no significant changes in nuclear perfusion scans. Although MR determined that resting radial motion and thickening of the target wall were significantly less than normal at baseline (p < 0.001), they improved significantly during follow-up (wall thickening: baseline, 30.6 +/- 11.7%; day 30, 41.2 +/- 13.3% and day 180, 44.2 +/- 11.9%, p = 0.01). The size of the underperfused myocardial area was 14.5 +/- 5.4% at baseline and was reduced to 6.3 +/- 2.8% at 30 days and 7.7 +/- 3.7% at 6 months (p < 0.001). CONCLUSIONS: This small phase I, open-label, uncontrolled study of MR functional and perfusion imaging in patients undergoing Biosense-guided LMR suggests a beneficial effect of this treatment strategy on myocardial function and perfusion. The efficacy of Biosense-guided LMR is being evaluated in a large phase II, randomized, blinded placebo-controlled trial with an MRI substudy (DIRECT).

Adult↗
PubMed1998

Colloidal Au-enhanced surface plasmon resonance immunosensing.

Surface plasmon resonance (SPR) biosensing using colloidal Au enhancement is reported. Immobilization of approximately 11-nm-diameter colloidal Au to an evaporated Au film results in a large shift in plasmon angle, a broadened plasmon resonance, and an increase in minimum reflectance. The incorporation of colloidal Au into SPR biosensing results in increased SPR sensitivity to protein-protein interactions when a Au film-immobilized antibody and an antigen-colloidal Au conjugate comprise the binding pair. A highly specific particle-enhanced analogue of a sandwich immunoassay is also demonstrated by complexing the Au particle to a secondary antibody. A tremendous signal amplification is observed, as addition of the antibody-Au colloid conjugate results in a 25-fold larger signal than that due to addition of a free antibody solution that is 6 orders of magnitude more concentrated. Picomolar detection of human immunoglobulin G has been realized using particle enhancement, with the theoretical limits for the technique being much lower. Finally, a quasi-linear relationship between particle coverage and plasmon angle shift is presented, thereby providing for a direct correlation between plasmon shift and solution antigen concentration. Together, these results represent significant advances in the generality and sensitivity of SPR as it is applied to biosensing.

Colloids↗
PubMed2005

Locally Addressable Electrochemical Patterning Technique (LAEPT) applied to poly(L-lysine)-graft-poly(ethylene glycol) adlayers on titanium and silicon oxide surfaces.

The protein-resistant polycationic graft polymer, poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), was uniformly adsorbed onto a homogenous titanium surface and subsequently subjected to a direct current (dc) voltage. Under the influence of an ascending cathodic and anodic potential, there was a steady and gradual loss of PLL-g-PEG from the conductive titanium surface while no desorption was observed on the insulating silicon oxide substrates. We have implemented this difference in the electrochemical response of PLL-g-PEG on conductive titanium and insulating silicon oxide regions as a biosensing platform for the controlled surface functionalization of the titanium areas while maintaining a protein-resistant background on the silicon oxide regions. A silicon-based substrate was micropatterned into alternating stripes of conductive titanium and insulating silicon oxide with subsequent PLL-g-PEG adsorption onto its surfaces. The surface modified substrate was then subjected to +1800 mV (referenced to the silver electrode). It was observed that the potentiostatic action removed the PLL-g-PEG from the titanium stripes without inducing any polyelectrolyte loss from the silicon oxide regions. Time-of-flight secondary ions mass spectroscopy and fluorescence microscopy qualitatively confirmed the PLL-g-PEG retention on the silicon oxide stripes and its absence on the titanium region. This method, known as "Locally Addressable Electrochemical Patterning Technique" (LAEPT), offers great prospects for biomedical and biosensing applications. In an attempt to elucidate the desorption mechanism of PLL-g-PEG in the presence of an electric field on titanium surface, we have conducted electrochemical impedance spectroscopy experiments on bare titanium substrates. The results showed that electrochemical transformations occurred within the titanium oxide layer; its impedance and polarization resistance were found to decrease steadily upon both cathodic and anodic polarization resulting in the polyelectrolyte desorption from the titanium surface.

Biosensing Techniques↗
PubMed2002

Microbial sensors on a respiratory basis for wastewater monitoring.

In respect of their rapidity, their online capabilities, and their moderate costs, biosensing systems generally offer an attractive alternative to the existing methods of water analysis. Additionally, one particular advantage of microbial biosensors is the ability to measure direct effects on living cells, e.g., their respiratory activity and its alteration caused by environmental pollutants. It is true that microbial sensors, often do not provide the optimum solution for the determination of individual analytes when compared to established physico-chemical analysis methods. However, these biosensing devices are predestined for the summary determination of environmentally relevant compounds and their complex effects, respectively. For this reason, microbial sensors allow an integral evaluation of the degree of environmental pollution including the interaction of various compounds. Moreover, in some cases specific metabolic pathways in microorganisms are used, resulting in the development of microbial sensors for the more selective analysis for those compounds or pollutants, which cannot be measured by simple enzyme reactions, e.g., the determination of aromatic compounds and heavy metals. This chapter gives an overview of microbiological biosensors on respiratory basis for the measurement of the following environmentally relevant compounds: inorganic N-compounds, heavy metals, organic xenobiotics and the estimation of sum parameters or so-called complex parameters such as BOD, ADOC, N-BOD, and the inhibition of nitrification.

Bacteria↗
PubMed2007

Recent advances in surface plasmon resonance based techniques for bioanalysis.

Surface plasmon resonance (SPR) is a powerful and versatile spectroscopic method for biomolecular interaction analysis (BIA) and has been well reviewed in previous years. This updated 2006 review of SPR, SPR spectroscopy, and SPR imaging explores cutting-edge technology with a focus on material, method, and instrument development. A number of recent SPR developments and interesting applications for bioanalysis are provided. Three focus topics are discussed in more detail to exemplify recent progress. They include surface plasmon fluorescence spectroscopy, nanoscale glassification of SPR substrates, and enzymatic amplification in SPR imaging. Through these examples it is clear to us that the development of SPR-based methods continues to grow, while the applications continue to diversify. Major trends appear to be present in the development of combined techniques, use of new materials, and development of new methodologies. Together, these works constitute a major thrust that could eventually make SPR a common tool for surface interaction analysis and biosensing. The future outlook for SPR and SPR-associated BIA studies, in our opinion, is very bright. Surface plasmon resonance (SPR) is a powerful and versatile spectroscopic method for biomolecular interaction analysis (BIA) and has been well reviewed in previous years. This updated 2006 review of SPR, SPR spectroscopy, and SPR imaging explores cutting-edge technology with a focus on material, method, and instrument development. A number of recent SPR developments and interesting applications for bioanalysis are provided. Three focus topics are discussed in more detail to exemplify recent progress. They include surface plasmon fluorescence spectroscopy, nanoscale glassification of SPR substrates, and enzymatic amplification in SPR imaging. Through these examples it is clear to us that the development of SPR-based methods continues to grow, while the applications continue to diversify. Major trends appear to be present in the development of combined techniques, use of new materials, and development of new methodologies. Together, these works constitute a major thrust that could eventually make SPR a common tool for surface interaction analysis and biosensing. The future outlook for SPR and SPR-associated BIA studies, in our opinion, is very bright.

Biological Assay↗
PubMed1992

Biosensors and flow injection analysis.

Combining flow injection analysis with a biosensor is a novel biosensing process which has allowed speedy and accurate analysis. Diagnostic analysis is the most important application for biosensing flow injection analysis, but other applications include bioprocess monitoring, analysis of food and agricultural products, as well as environmental analysis. In addition, the analysis of compounds, such as explosives and abused drugs, and monitoring of Salmonella, the microorganism that causes food poisoning, have been reported.

Animals↗
PubMed2005

Flow-injection enzymatic analysis for glycerol and triacylglycerol.

A flow-injection enzymatic analytical system was developed for determination of glycerol and triacylglycerol based on enzymatic reactions in capillary followed by electrochemical detection. The hydrogen peroxide produced from the enzyme reaction was monitored by a platinum-based electrochemical probe. Different immobilization strategies on silica support were studied. The best and most effective configuration found for the measurement of glycerol and triacylglycerols in this system was the tandem connection of a lipase column and a silica-fused capillary column coimmobilized with glycerokinase (GK) and glycerol-3-phosphate oxidase (GPO). Lipase helps the breakdown of triacylglycerol to yield free fatty acids and glycerol, while glycerokinase catalyzes the adenosine-5-triphosphate-dependent phosphorylation of glycerol to yield alpha-glycerol phosphate, which can subsequently be oxidized by 3-glycerol phosphate oxidase to produce hydrogen peroxide. Response-surface methodology (RSM) was applied to optimize the proposed system for glycerol. Experiment settings were designed by central composite design to investigate the combined effects of pH, flow rate, reaction temperature, and ATP concentration on collected signals. The fitted model, per RSM, showed that the optimum conditions of the system are 2 mM ATP in 0.1 M carbonate buffer (pH 11.0), flow rate of 0.18 mL/min, temperature of 35 degrees C, 20 microL of sample injection, and applied voltage of 0.650 V. The proposed biosensing system using lipase, GK, and GPO exhibited a flow-injection analysis peak response of 2.5 min and a detection limit of 5 x 10(-5) M glycerol (S/N = 3) with acceptable reproducibility (CV < 4.30%). It also had linear working ranges from 10(-4) to 10(-2) M for glycerol and from 10(-3) to 10(-2) M for triacylglycerol. The capillary enzyme reactor was stable up to 2 months in continuous operation, and it was possible to analyze up to 15 samples per hour. The present biosensing system holds promise for on-line detection of triacylglycerol in serum and glycerol content in fermented products.

Biosensing Techniques↗
PubMed2006

Novel biphasic separations utilising highly selective molecularly imprinted polymers as biorecognition solvent extraction agents.

Molecularly imprinted polymers (MIPs) represent a class of artificial receptors that promise an environmentally robust alternative to naturally occurring biorecognition elements of biosensing devices and systems. However, in general, the performance of conventional MIPs in aqueous environments is poor. In the study reported here, this limitation has been addressed by the novel application of MIPs as a solvent extraction solid phase in a biphasic solvent system. This paper describes a previously unreported use of MIPs as solvent extraction reagents, their successful application to aqueous sample media and the opportunities for utilisation of this unique system in novel biosensing and separation procedures. This study demonstrates the development of a novel biphasic solvent system utilising MIP in the extracting phase to enhance both efficiency and selectivity of a simple two phase liquid extraction. Monodisperse propranolol imprinted polymer microspheres [p(divinylbenzene-co-methacrylic acid)] were prepared by precipitation polymerisation. Initially, the affinity of the polymers for (R,S)-propranolol was assessed by established techniques whereby the MIP demonstrated greater affinity for the template than did the non-imprinted control polymer (NIP). Importantly, MIP performance was also assessed using the novel dual solvent system. The depletion of (R,S)-propranolol from the aqueous phase into the polymer containing organic phase was determined. When compared to control extractions containing no polymer the presence of MIP in the extracting solvent phase resulted in an increased extraction of (R,S)-propranolol from the aqueous phase. Importantly, this extraction was significantly greater in the presence of MIP when compared to NIP. This unique principle generates opportunities for MIP based extractions and chemical enrichments in industrial applications, offering commercial, ecological and practical advantages to traditional solvent extraction techniques. The technique is readily transferable to analytical microsystems utilising MIP recognition elements generating promising opportunities for MIP based sensing of aqueous sample media.

Biosensing Techniques↗
PubMed2006

Reagentless biosensor for hydrogen peroxide based on immobilization of protein in zirconia nanoparticles enhanced grafted collagen matrix.

A novel matrix, zirconia nanoparticles enhanced grafted collagen (ZrO2-grafted collagen) hybrid composite, for immobilization of protein and biosensing was developed. The scanning electron microscopy, UV-vis and Fourier transform infrared spectra, and electrochemical measurements showed that the matrix was well biocompatible and could retain the bioactivity of immobilized protein to a large extent. The direct electron transfer of the immobilized myoglobin (Mb) exhibited a couple of stable and well-defined redox peaks with the formal potential of -336 mV (versus SCE) in 0.1M pH 7.0 PBS. This matrix could accelerate the electron transfer between Mb and the electrode with a surface-controlled process and an electron transfer rate constant of 3.58+/-0.35s-1 at 10-500 mVs-1. The Mb immobilized in the matrix showed a high thermal stability up to 70 degrees C and an electrocatalytic activity to the reduction of hydrogen peroxide (H2O2) without the help of an electron mediator. The linear response range of the biosensor to H2O2 concentration was from 1.0 to 85.0 microM with the limit of detection of 0.63 microM at a signal-to-noise ratio of 3sigma. The biosensor exhibited high sensitivity, acceptable stability and reproducibility. This work opened a way for the further study on the direct electron transfer and biosensing application of the immobilized protein in collagen-related matrices.

Biosensing Techniques↗
PubMed2007

Real-time detection of Escherichia coli O157:H7 sequences using a circulating-flow system of quartz crystal microbalance.

A DNA piezoelectric biosensing method for real-time detection of Escherichia coli O157:H7 in a circulating-flow system was developed in this study. Specific probes [a 30-mer oligonucleotide with or without additional 12 deoxythymidine 5'-monophosphate (12-dT)] for the detection of E. coli O157:H7 gene eaeA, synthetic oligonucleotide targets (30 and 104 mer) and PCR-amplified DNA fragments from the E. coli O157:H7 eaeA gene (104 bp), were used to evaluate the efficiency of the probe immobilization and hybridization with target DNA in the circulating-flow quartz crystal microbalance (QCM) device. It was found that thiol modification on the 5'-end of the probes was essential for probe immobilization on the gold surface of the QCM device. The addition of 12-dT to the probes as a spacer, significantly enhanced (P<0.05) the hybridization efficiency (H%). The results indicate that the spacer enhanced the H% by 1.4- and 2-fold when the probes were hybridized with 30- and 104-mer targets, respectively. The spacer reduced steric interference of the support on the hybridization behavior of immobilized oligonucleotides, especially when the probes hybridized with relatively long oligonucleotide targets. The QCM system was also applied in the detection of PCR-amplified DNA from real samples of E. coli O157:H7. The resultant H% of the PCR-amplified double-strand DNA was comparable to that of the synthetic target T-104AS, a single-strand DNA. The piezoelectric biosensing system has potential for further applications. This approach lays the groundwork for incorporating the method into an integrated system for rapid PCR-based DNA analysis.

Adhesins, Bacterial↗
PubMed2000

Capillary electrophoresis coupled to biosensor detection.

The present review highlights some modern aspects of biosensor revelation, a detection method which has already found a large number of applications in healthcare, food industry and environmental analysis. First, the concept of bio-recognition, which is at the heart of biosensor technology, is discussed, with emphasis on host-guest-like recognition mechanisms. This detection device has been successfully coupled, in its first applications, to chromatographic columns, which allow a high resolution of complex mixtures of analytes prior to interaction with the biosensing unit. The properties of the transducing elements, which should generate a signal (e.g., electrochemical, thermal, acoustic, optical) of proper intensity and of relative fast rise, are additionally evaluated and discussed. The review then focuses on potential applications of biosensing units in capillary electrophoresis (CE) devices. CE appears to be an excellent separation methodology to be coupled to biosensor detection, since it is based on miniaturized electrophoretic chambers, fast analysis times, complete automation in sample handling and data treatment and requires extremely small sample volumes. Although only a few applications of CE-based biosensors have been described up to the present, it is anticipated that this hyphenated technique could have a considerable expansion in the coming years.

Biosensing Techniques↗
PubMed2003

Oriented and vectorial immobilization of linear M13 dsDNA between interdigitated electrodes--towards single molecule DNA nanostructures.

The ability to control molecules at a resolution well below that offered by photolithography has gained much interest recently. DNA is a promising candidate for this task since it offers excellent specificity in base-pairing combined with addressability at the nanometer scale. New applications in biosensing, e.g. interaction analysis at the single molecule level, or nanobiotechnology, e.g. ultradense DNA microarrays, have been devised that rely on stretched DNA bridges. The basic technology required is the ability to deposit spatially defined, stretched DNA-bridges between anchoring structures on surfaces. In this paper we present two techniques for spanning 2 microm long dsDNA bridges between neighboring interdigitated electrodes (IDEs). The extended DNA used was linearized M13 dsDNA (M13mp18 7231 bp, ca. 2.5 microm length), either unmodified, or with chemical modifications at both ends. The first approach is based on the dielectrophoretic (DEP) concentration and alignment of linearized wild-type dsDNA. IDEs with 1.7 microm spacing are driven with an AC voltage around 1 MHz leading to field strengths in the order of 1 MV m(-1). The dsDNA is polarized and linearized by the force field and accumulates in the gap between two neighboring electrodes. This process is reversible and was visualized by fluorescence staining of M13 DNA using PicoGreen, as intercalating dye. The resulting dsDNA bridges and their orientation are discernible under the fluorescence microscope using fluorescent particles of different color. The particles are tagged with sequence specific peptide nucleic acid (PNA) probes that bind to the DNA double strand at specific sites. The second approach is based on asymmetric electrochemical modification of a gold IDE with 2.0 microm spacings followed by spontaneous or stimulated deposition of a chemically modified M13-DNA. One side of the IDE was selectively coated with streptavidin by electropolymerization of a novel hydrophilic conductive polymer in the presence of the binding protein. The second side was modified with gold nanoparticles by reductive plating from aqueous gold chloride solution. An asymmetric double stranded (ds) M13 DNA carrying a 5'-thiol group at one end and a 5'-biotin at the other end was obtained by polymerase chain reaction (PCR) using two differently labeled primers. For DNA bridges to form spontaneously the modified IDE was incubated over night with a 50 nM solution of the modified M13 DNA. Potential applications of DNA-bridge formation in biosensing and biotechnology are discussed.

Adsorption↗
PubMed2004

Novel biosensor chip for simultaneous detection of DNA-carcinogen adducts with low-temperature fluorescence.

A monoclonal antibody (MAb)-gold biosensor chip with low-temperature laser-induced fluorescence detection for analysis of DNA-carcinogen adducts is described. Optimization of the detection limit, dynamic range, and biosensing applicability of the MAb-gold biosensor chip was achieved by: (1) using dithiobis(succinimidyl propionate (DSP)) as a protein linker and (2) employing recombinant protein A to provide oriented immobilization of the MAbs. The use of DSP, which has a short methylene chain length, led to faster protein binding kinetics and higher protein surface density than a longer dithiobis(succinimidyl undecanoate) (DSU) linker. The incorporation of recombinant protein A increased the distance between the oriented MAb-bound analytes and the gold surface. The increased distance minimized fluorescence quenching, resulting in about a 10-fold increase in the fluorescence signal in comparison with a chip without protein A. The improved chip architecture was used to demonstrate that biosensing of two structurally similar benzo[a]pyrene (BP)-derived DNA adducts, BP-6-N7Gua and BP-diolepoxide-10-N2dG, bound to two specific MAbs immobilized from a mixture at the same address on the chip, is feasible. These mutagenic adducts are formed by one-electron oxidation and monooxygenation pathways, and are depurinating and stable DNA adducts, respectively. It is shown that the DNA adducts can be easily identified at the same address using time-resolved, low-temperature laser-based fluorescence spectroscopy. The current limit of detection is in the low femtomole range. These results indicate that a single biosensor chip consisting of a Au/DSP/protein A/MAb nano-assembly, with analyte-specific MAbs and low-temperature fluorescence detection should be suitable for simultaneous detection and quantitation of the above adducts, as well as the luminescent antigens for which selective MAbs exist.

Benzo(a)pyrene↗
PubMed1997

Nucleic-acid immobilization, recognition and detection at chronopotentiometric DNA chips.

Wide-scale DNA testing requires the development of fast, small, easy-to-use biosensing devices. Various synthetic oligonucleotides and DNA have thus been immobilized onto microfabricated thick-film carbon transducers for performing several new nucleic-acid assay protocols. These include hybridization detection of nucleic acid sequences, determination of small molecules (drugs, pollutants) based on their collection into the dsDNA layer or via monitoring their effect upon the intrinsic DNA oxidation signal, and direct adsorptive stripping measurements of ultratrace levels of nucleic acids. Transduction of these DNA recognition processes is accomplished by a new highly-sensitive constant-current stripping chronopotentiometric operation. Comparison to traditional electrodes indicates that the biosensing performance is not compromised by the use of mass-producible disposable transducers. Such thick-film DNA biosensors have been coupled to a compact, user-friendly, hand-held analyzer. Applicability for the detection of sequences from M. tuberculosis and HIV-1 DNAs is illustrated. Such activity in the author's laboratory, aimed at developing DNA-coated screen-printed electrodes, is reviewed.

Biosensing Techniques↗
PubMed2001

Guided shear horizontal surface acoustic wave sensors for chemical and biochemical detection in liquids.

The design and performance of guided shear horizontal surface acoustic wave (guided SH-SAW) devices on LiTaO3 substrates are investigated for high-sensitivity chemical and biochemical sensors in liquids. Despite their structural similarity to Rayleigh SAW, SH-SAWs often propagate slightly deeper within the substrate, hence preventing the implementation of high-sensitivity detectors. The device sensitivity to mass and viscoelastic loading is increased using a thin guiding layer on the device surface. Because of their relatively low shear wave velocity, various polymers including poly(methyl methacrylate) (PMMA) and cyanoethyl cellulose (cured or cross-linked) are investigated as the guiding layers to trap the acoustic energy near the sensing surface. The devices have been tested in biosensing and chemical sensing experiments. Suitable design principles for these applications are discussed with regard to wave guidance, electrical passivation of the interdigital transducers from the liquid environments, acoustic loss, and sensor signal distortion. In biosensing experiments, using near-optimal PMMA thickness of approximately 2 microm, mass sensitivity greater than 1500 Hz/(ng/mm2) is demonstrated, resulting in a minimum detection limit less than 20 pg/mm2. For chemical sensor experiments, it is found that optimal waveguide thickness must be modified to account for the chemically sensitive layer which also acts to guide the SH-SAW. A detection limit of 780 (3 x peak-to-peak noise) or 180 ppb (3 x rms noise) is estimated from the present measurements for some organic compounds in water.

Acoustics↗