Biological sample analysis with immunoaffinity solid-phase microextraction

Unveiling the power of MXenes: Solid lubrication perspectives and future directions

The interaction between two surfaces leads to the generation of friction and wear of material. Friction and wear are some of the major challenges that may readily be overcome by the third part of tribology called lubrication. Utilizing solid lubricants including polymers, carbon-based materials, soft metals, transition metal dichalcogenides, along with their potential benefits and drawbacks in dry environments can reduce friction. Recently, an emerging class of two-dimensional (2D) transition metal nitrides, carbides or carbonitrides commonly known as MXenes have emerged as an attractive alternative for solid lubrication because of their ability to establish wear-resistant tribo layers and well as low friction and shear strength. Furthermore, the inherent hydrophilic nature of these substances has led to limited dispersion stability and phase compatibility when combined with pure base oils. As a result, their potential use as solid lubricants and lubricant additives has been impeded. To address this issue and enhance the applicability of MXenes as solid lubricants, their surface modification can be an attractive tool. Therefore, this review provides a succinct summary of the current state-of-the-art in surface functionalization of MXenes, a subject that has not yet been thoroughly addressed. Further, the mechanical behavior of MXenes and composites has been discussed, followed by the potential of MXenes as a solid lubricant at micro- and macro-scale. Finally, the existing opportunities and challenges of the research area have been discussed with possible future research directions. We believe, this article will be a valuable resource for MXenes and opens the door to improve the chemical, physical and mechanical properties of MXenes in various applications, such as solid lubrication.

Surface chemistry applications and development of immunosensors using electrochemical impedance spectroscopy: A comprehensive review

Immunosensors are promising alternatives as detection platforms for the current gold standards methods. Electrochemical immunosensors have already proven their capability for the sensitive, selective, detection of target biomarkers specific to COVID-19, varying cancers or Alzheimer's disease, etc. Among the electrochemical techniques, electrochemical impedance spectroscopy (EIS) is a highly sensitive technique which examines the impedance of an electrochemical cell over a range of frequencies. There are several important critical requirements for the construction of successful impedimetric immunosensor. The applied surface chemistry and immobilisation protocol have impact on the electroanalytical performance of the developed immunosensors. In this Review, we summarise the building blocks of immunosensors based on EIS, including self-assembly monolayers, nanomaterials, polymers, immobilisation protocols and antibody orientation.

A highly sensitive fluorescent sensor for ammonia detection based on aggregation-induced emission luminogen-doped liquid crystals

As a toxic substance, ammonia can cause serious irritation to the human respiratory system and lungs. Although many detection techniques have been reported, most of them have drawbacks, such as expensive devices and complex and time-consuming fabrication processes. Thus, it is important to develop a simple method for ammonia detection. In this paper, we demonstrate a highly sensitive fluorescent sensor for ammonia detection based on aggregation-induced emission luminogen-doped liquid crystals without the use of polarizers. The homeotropic orientation of the liquid crystals on a modified substrate can be disturbed by ammonia, resulting in the fluorescence intensity change of an aggregation-induced emission luminogen. This aggregation-induced emission luminogen-doped liquid crystal-based fluorescent sensor for ammonia detection exhibited a low detection limit of 5.4 ppm, which is 3 times lower than previously reported liquid crystal-based optical sensors. The detection range is also broad from 0 ppm to 1600 ppm. Meanwhile, this sensor can be applied to detect aqueous ammonia with a low limit of detection of 1.8 ppm. The proposed fluorescent sensor for ammonia detection based on an aggregation-induced emission luminogen-doped liquid crystal is highly sensitive, highly selective, simple, and low cost with wide potential applications in chemical and biological fields. This strategy of designing a liquid crystal fluorescent sensor provides an inspiring stage for other toxic chemical substrates by changing specific decorated molecules.

Imprinted Photonic Crystal-Film-Based Smartphone-Compatible Label-Free Optical Sensor for SARS-CoV-2 Testing

The coronavirus disease (COVID-19) caused by SARS-CoV-2 has caused a global pandemic. To manage and control the spread of the infection, it is crucial to develop and implement technologies for the early identification of infected individuals and rapid informatization in communities. For the realization of such a technology, a widely available and highly usable sensor for sensitive and specific assay of the virus plays a fundamental role. In this study, we developed an optical sensor based on an imprinted photonic crystal film (IPCF) for quick, simple, and cost-effective detection of SARS-CoV-2 spike protein in artificial saliva. Our IPCF sensor enabled label-free and highly sensitive detection with a smartphone-equipped optical setup. The IPCF surface was functionalized with an anti-SARS-CoV-2 spike protein antibody for immunoassay. We evaluated the specificity and sensitivity of the IPCF sensor for quantitative detection of the spike protein in artificial saliva using simple reflectometry with a spectrometer-equipped optical setup. Specific and quantitative detection of the spike protein was successfully achieved, with a low detection limit of 429 fg/mL. In the demonstration of reflectometric detection with a smartphone-equipped setup, the sensitivity was comparable with that with a spectrometer-equipped setup. The test result is returned immediately and can be saved to cloud storage. In addition, it costs less than USD 1 for one IPCF to be used for diagnosis. Thus, the developed IPCF has the potential to realize a widely available and highly usable sensor.

Carbonic anhydrase modification for carbon management

Carbonic anhydrase modification (chemical and biological) is an attractive strategy for its diverse application to accelerate the absorption of CO₂ from a flue gas with improved activity and stability. This article reports various possibilities of CA modification using metal-ligand homologous chemistry, cross-linking agents, and residue- and group-specific and genetic modifications, and assesses their role in carbon management. Chemically modified carbonic anhydrase is able to improve the absorption of carbon dioxide from a gas stream into mediation compounds with enhanced sequestration and mineral formation. Genetically modified CA polypeptide can also increase carbon dioxide conversion. Chemical modification of CA can be categorized in terms of (i) residue-specific modification (involves protein-ligand interaction in terms of substitution/addition) and group-specific modifications (based on the functional groups of the target CA). For every sustainable change, there should be no/limited toxic or immunological response. In this review, several CA modification pathways and biocompatibility rules are proposed as a theoretical support for emerging research in this area.

Development of a new method for sampling and monitoring oncology staff exposed to cyclophosphamide drug

Treatment using cytotoxic drugs is considered to be the most common treatment for cancers. However, the widespread use of these drugs on the health status of the staff at the oncology department has become a great concern. Due to challenges of sampling and analysis of cytotoxic drugs, the aim of this study was to development a novel practical method called Needle trap devices (NTD) for sampling and analysis of personal exposure to cyclophosphamide drug. The sampler consisted of a stainless steel hyper needle gauge 21 of length 9 cm packed with Carboxen 1000 for adsorbing cyclophosphamide. A total of 41 samples of staff's air breathing zone in different wards of the oncology department were taken with the sampler. Samples were analyzed by gas chromatography coupled with electron capture detector (ECD). Linear range concentration was 212-1062 μg/m(3), and LOD and LOQ were 100 and 191 μg/m(3), respectively. The mean inter-day and intra-day coefficient variations for standards within linear range concentration were 8.9 and 4.8 %, respectively. Detectable levels of cyclophosphamide were measured in 31.7 % of air samples. The developed method is user-friendly, quick, and precise for sampling of airborne cyclophosphamide. The results showed that some staff of the oncology department were exposed to the carcinogenic drug and their health were at risk. Since carcinogens do not have a threshold and oncology staffs with their continuous exposure might be at risk, therefore, proper work practice and adequate control measures are essential to ensure their wellbeing.

A nanoporous carbon material derived from pomelo peels as a fiber coating for solid-phase microextraction

A novel nanoporous carbon derived from a biomass source was prepared and used as an SPME fiber coating.

Enhanced In Vitro Biocompatibility of Chemically Modified Poly(dimethylsiloxane) Surfaces for Stable Adhesion and Long-term Investigation of Brain Cerebral Cortex Cells

Studies on the mammalian brain cerebral cortex have gained increasing importance due to the relevance of the region in controlling critical higher brain functions. Interactions between the cortical cells and surface extracellular matrix (ECM) proteins play a pivotal role in promoting stable cell adhesion, growth, and function. Poly(dimethylsiloxane) (PDMS) based platforms have been increasingly used for on-chip in vitro cellular system analysis. However, the inherent hydrophobicity of the PDMS surface has been unfavorable for any long-term cell system investigations due to transitory physical adsorption of ECM proteins on PDMS surfaces followed by eventual cell dislodgement due to poor anchorage and viability. To address this critical issue, we employed the (3-aminopropyl)triethoxysilane (APTES) based cross-linking strategy to stabilize ECM protein immobilization on PDMS. The efficiency of surface modification in supporting adhesion and long-term viability of neuronal and glial cells was analyzed. The chemically modified surfaces showed a relatively higher cell survival with an increased neurite length and neurite branching. These changes were understood in terms of an increase in surface hydrophilicity, protein stability, and cell-ECM protein interactions. The modification strategy could be successfully applied for stable cortical cell culture on the PDMS microchip for up to 3 weeks in vitro.

The effects of poly(dimethylsiloxane) surface silanization on the mesenchymal stem cell fate

In recent years, poly(dimethylsiloxane) (PDMS)-based microfluidic devices have become very popular for on-chip cell investigation. Maintenance of mammalian cell adhesion on the substrate surface is crucial in determining the cell viability, proliferation and differentiation. However, the inherent hydrophobicity of PDMS is unfavourable for cell culture, causing cells to eventually dislodge from the surface. Although physically adsorbed matrix proteins can promote initial cell adhesion, this effect is usually short-lived. To address this critical issue, in this study, we employed (3-aminopropyl) triethoxy silane (APTES) and cross-linker glutaraldehyde (GA) chemistry to immobilize collagen type 1 (Col1) on PDMS. These modified surfaces are highly efficient to support the adhesion of mesenchymal stem cells (MSCs) with no deterioration of their potency. Significant changes of the native PDMS surface properties were observed with the proposed surface functionalization, and MSC adhesion was improved on PDMS surfaces modified with APTES + GA + Protein. Therefore, this covalent surface modification could generate a more biocompatible platform for stabilized cell adhesion. Furthermore, this modification method facilitated long-term cell attachment, which is favourable for successful induction of osteogenesis and cell sheet formation with an increased expression of osteogenic biomarkers and comparable extracellular matrix (ECM) constituent biomarkers, respectively. The surface silanization can be applied to PDMS-based microfluidic systems for long-term study of cellular development. Similar strategies could also be applied to several other substrate materials by appropriate combinations of self-assembled monolayers (SAMs) and ECM proteins.

Aptamer-functionalized solid phase microextraction-liquid chromatography/tandem mass spectrometry for selective enrichment and determination of thrombin

In this publication, a novel solid phase microextraction (SPME) coating functionalized with a DNA aptamer for selective enrichment of a low abundance protein from diluted human plasma is described. This approach is based on the covalent immobilization of an aptamer ligand on electrospun microfibers made with the hydrophilic polymer poly(acrylonitrile-co-maleic acid) (PANCMA) on stainless steel rods. A plasma protein, human α-thrombin, was employed as a model protein for selective extraction by the developed Apt-SPME probe, and the detection was carried out with liquid chromatography/tandem mass spectrometry (LC-MS/MS). The SPME probe exhibited highly selective capture, good binding capacity, high stability and good repeatability for the extraction of thrombin. The protein selective probe was employed for direct extraction of thrombin from 20-fold diluted human plasma samples without any other purification. The Apt-SPME method coupled with LC-MS/MS provided a good linear dynamic range of 0.5-50 nM in diluted human plasma with a good correlation coefficient (R(2)=0.9923), and the detection limit of the proposed method was found to be 0.30 nM. Finally, the Apt-SPME coupled with LC-MS/MS method was successfully utilized for the determination of thrombin in clinical human plasma samples. One shortcoming of the method is its reduced efficiency in undiluted human plasma compared to the standard solution. Nevertheless, this new aptamer affinity-based SPME probe opens up the possibility of selective enrichment of a given targeted protein from complex sample either in vivo or ex vivo.

Surface chemical modification of poly(dimethylsiloxane) for the enhanced adhesion and proliferation of mesenchymal stem cells

The surface chemistry of materials has an interactive influence on cell behavior. The optimal adhesion of mammalian cells is critical in determining the cell viability and proliferation on substrate surfaces. Because of the inherent high hydrophobicity of a poly(dimethylsiloxane) (PDMS) surface, cell culture on these surfaces is unfavorable, causing cells to eventually dislodge from the surface. Although physically adsorbed matrix proteins can promote initial cell adhesion, this effect is usually short-lived. Here, (3-aminopropyl)triethoxy silane (APTES) and cross-linker glutaraldehyde (GA) chemistry was employed to immobilize either fibronectin (FN) or collagen type 1 (C1) on PDMS. The efficiency of these surfaces to support the adhesion and viability of mesenchymal stem cells (MSCs) was analyzed. The hydrophobicity of the native PDMS decreased significantly with the mentioned surface functionalization. The adhesion of MSCs was mostly favorable on chemically modified PDMS surfaces with APTES + GA + protein. Additionally, the spreading area of MSCs was significantly higher on APTES + GA + C1 surfaces than on other unmodified/modified PDMS surfaces with C1 adsorption. However, there were no significant differences in the MSC spreading area on the unmodified/modified PDMS surfaces with FN adsorption. Furthermore, there was a significant increase in cell proliferation on the PDMS surface with APTES + GA + protein functionalization as compared to the PDMS surface with protein adsorption only. Therefore, the covalent surface chemical modification of PDMS with APTES + GA + protein could offer a more biocompatible platform for the enhanced adhesion and proliferation of MSCs. Similar strategies can be applied for other substrates and cell lines by appropriate combinations of self-assembly monolayers (SAMs) and extracellular matrix proteins.

Application of a new microcantilever biosensor resonating at the air-liquid interface for direct insulin detection and continuous monitoring of enzymatic reactions

Here we describe the application of a recently developed high-resolution microcantilever biosensor resonating at the air-liquid interface for the continuous detection of antigen-antibody and enzyme-substrate interactions. The cantilever at the air-liquid interface demonstrated 50% higher quality factor and a 5.7-fold increase in signal-to-noise-ratio (SNR) compared with one immersed in the purified water. First, a label-free detection of a low molecular weight protein (insulin, 5.8 kDa) in physiological concentration was demonstrated. The liquid facing side of the cantilever was functionalized by coating its surface with insulin antibodies, while the opposite side was exposed to air. The meniscus membrane at the micro-slit around the cantilever sustained the liquid in the microchannel. After optimizing the process of surface functionalization, the resonance frequency shift was successfully measured for insulin solutions of 0.4, 2.0, and 6.3 ng ml(-1). To demonstrate additional application of the device for monitoring enzymatic protein degradation, the liquid facing microcantilever surface was coated with human recombinant SOD1 (superoxide dismutase 1) and exposed to various concentrations of proteinase K solution, and the kinetics of the SOD1 digestion was continuously monitored. The results showed that it is a suitable tool for sensitive protein detection and analysis.

High-resolution cantilever biosensor resonating at air-liquid in a microchannel

We have developed a highly mass-sensitive cantilever resonating at the interface of air and liquid. The cantilever is applicable as a biosensor by measuring its resonance frequency shift associated with the selective trapping of target molecules. One surface of the cantilever facing to the liquid is functionalized for label-free detection, while the opposite side is exposed to air to improve the resonance characteristics, such as the quality factor. The quality factor at resonance is 15, which is 50% higher than the same cantilever in liquid. The beam was excited through the photothermal effect of a power modulated laser and detected by laser Doppler velocimetry. Due to the proposed configuration, the signal-to-noise-ratio is 5.7 times larger than the completely submerged case. A micro-slit around the cantilever separates the air and liquid phases at a meniscus. We analyzed the cantilever motion including the meniscus membrane, and examined the effect of surface tension by applying various solutions. A slit width of 6 μm was found to give the best performance within the few prototypes. We measured the covalent immobilization of antibody molecules on a cantilever surface for three different concentrations: 20, 40, and 80 μg ml(-1). The kinetics measured by both resonance frequency shift of the cantilever and fluorescent intensity showed good agreement.

The development of biosensor with imaging ellipsometry

The concept of biosensor with imaging ellipsometry was proposed about ten years ago. It has become an automatic analysis technique for protein detection with merits of label-free, multi-protein analysis, and real-time analysis for protein interaction process, etc. Its principle, and related technique units, such as micro-array, micro-fluidic and bio-molecule interaction cell, sampling unit and calibration for quantitative detection as well as its applications in biomedicine field are presented here.

A study of the performance characteristics of immunoaffinity solid phase microextraction probes for extraction of a range of benzodiazepines

Immunoaffinity solid phase microextraction (SPME) probes have been developed with antibodies specific for the benzodiazepine class of drugs, covalently immobilized to glass rods. This involved both purification of the polyclonal antibodies to isolate the drug-specific fraction, and optimization of the immobilization procedure. Such probes have been used previously for the extraction of 7-aminoflunitrazepam. This article presents a comprehensive study of their performance and characteristics beyond that described previously, and an evaluation of their application to additional benzodiazepines. The influence of non-specific drug binding (nsb) was determined, with the result that nsb was found to be insignificant for the probes when used in their dynamic range. Immobilized antibodies had specific affinities in the range of 10(9)-10(10)M(-1). Cross-reactivity was evaluated both for a range of benzodiazepines as well as a structurally unrelated molecule (erythromycin). For analysis of benzodiazepines individually or in the presence of erythromycin, limits of detection were 0.001-0.015 ng/mL depending on the antibody, and the dynamic range (based on 80-90% antigenic site occupancy) extended to 0.2-2 ng/mL.

Strategies for interfacing solid-phase microextraction with liquid chromatography

Solid-phase microextraction (SPME) techniques are equally applicable to both volatile and non-volatile analytes, but the progress in applications to gas-phase separations has outpaced that of liquid-phase separations. The interfacing of SPME to gas chromatographic equipment has been straight-forward, requiring little modification of existing equipment. The requirement of solvent desorption for non-volatile or thermally labile analytes has, however, proven challenging for interfacing SPME with liquid-phase separations. Numerous options to achieve this have been described in the literature over the past decade, with applications in several different areas of analysis. To date, no single strategy or interface device design has proven optimal. During method development analysts must select the most appropriate interfacing technique among the options available. Out of these options three general strategies have emerged: (1) use of a manual injection interface tee; (2) in-tube SPME; and (3) off-line desorption followed by conventional liquid injection. In addition, there has been interest in coupling SPME directly to electrospray ionisation and matrix-assisted laser desorption ionisation (MALDI) for mass spectrometry. Several examples of each of these strategies are reviewed here, and an overview of their use and application is presented.

Application of solid-phase microextraction in analytical toxicology

Solid-phase microextraction (SPME) is a miniaturized and solvent-free sample preparation technique for chromatographic-spectrometric analysis by which the analytes are extracted from a gaseous or liquid sample by absorption in, or adsorption on, a thin polymer coating fixed to the solid surface of a fiber, inside an injection needle or inside a capillary. In this paper, the present state of practical performance and of applications of SPME to the analysis of blood, urine, oral fluid and hair in clinical and forensic toxicology is reviewed. The commercial coatings for fibers or needles have not essentially changed for many years, but there are interesting laboratory developments, such as conductive polypyrrole coatings for electrochemically controlled SPME of anions or cations and coatings with restricted-access properties for direct extraction from whole blood or immunoaffinity SPME. In-tube SPME uses segments of commercial gas chromatography (GC) capillaries for highly efficient extraction by repeated aspiration-ejection cycles of the liquid sample. It can be easily automated in combination with liquid chromatography but, as it is very sensitive to capillary plugging, it requires completely homogeneous liquid samples. In contrast, fiber-based SPME has not yet been performed automatically in combination with high-performance liquid chromatography. The headspace extractions on fibers or needles (solid-phase dynamic extraction) combined with GC methods are the most advantageous versions of SPME because of very pure extracts and the availability of automatic samplers. Surprisingly, substances with quite high boiling points, such as tricyclic antidepressants or phenothiazines, can be measured by headspace SPME from aqueous samples. The applicability and sensitivity of SPME was essentially extended by in-sample or on-fiber derivatization. The different modes of SPME were applied to analysis of solvents and inhalation narcotics, amphetamines, cocaine and metabolites, cannabinoids, methadone and other opioids, fatty acid ethyl esters as alcohol markers, gamma-hydroxybutyric acid, benzodiazepines, various other therapeutic drugs, pesticides, chemical warfare agents, cyanide, sulfide and metal ions. In general, SPME is routinely used in optimized methods for specific analytes. However, it was shown that it also has some capacity for a general screening by direct immersion into urine samples and for pesticides and other semivolatile substance in the headspace mode.

Determination of drug plasma protein binding by solid phase microextraction

The plasma protein binding of drugs has been shown to have significant effects on the quantitative relationship between clinical pharmacokinetics and pharmacodynamics. In many clinical situations, measurement of the total drug concentration does not provide the needed information concerning the unbound fraction of drug in plasma, which is available for pharmacodynamic action. Therefore, the accurate determination of unbound plasma drug concentrations is important in understanding drug action. Many methodologies exist for determining the extent of plasma protein binding, but different methods produce a rather wide range of results for the same compound at the same concentration level. The solid phase microextraction (SPME) method reported in the present study attempts to eliminate many experimental variables that could lead to the lack of reproducibility, such as the variable content of organic solvent or ionic strength in plasma, pH shifts, and volume shifts. Five well-known drugs were chosen to study plasma protein binding: ibuprofen, warfarin, verapamil, propranolol, and caffeine, with high, intermediate and low binding properties. Dilution of plasma with isotonic PBS or incubation with 10% CO(2) in the atmosphere was found to compensate for changes in pH during incubation. The data obtained using these pH-controlled methods correlate well with the average values of plasma protein binding found in the literature. SPME, which uses an extraction phase that dissolves or adsorbs the drug of interest and rejects proteins, overcomes several limitations of currently available techniques and is a thermodynamically sound method, since the measurements are always performed at equilibrium. Compared to other methods, SPME offers several advantages: small sample size, short analysis time, possibility to automate, and ability to directly study complex samples.

Development of immunoaffinity solid phase microextraction probes for analysis of sub ng/mL concentrations of 7-aminoflunitrazepam in urine

We report on the development of solid phase microextraction probes for drug analysis, prepared with antibodies specific for benzodiazepines covalently immobilized to the surface. In the technique, immobilized antibody probes are exposed to a sample containing the drug for 30 min. Extracted drugs are subsequently desorbed from the probes in 500 microL of methanolic desorption solution, which is dried, reconstituted in a small volume of injection solution and analysed by LC-MS/MS. The antibodies were characterized both before and after immobilization, to facilitate the rational selection of antibodies for such analyses. Polyclonal and monoclonal antibodies were compared as was the impact of affinity purification of the polyclonal antibody to isolate the drug-specific fraction. The probes were evaluated for utility in analyzing 7-aminoflunitrazepam at sub ng/mL concentrations in urine, which is expected to be found several days after a single oral dose of 2 mg of flunitrazepam. Such analyses are required in monitoring for abuse of this drug, both in terms of 'club drug' use and in cases of drug-facilitated sexual assault. In these cases drug concentrations in blood and urine are much lower than in chronic abuse cases and are difficult to analyse by conventional methods. The method developed has a limit of detection of 0.02 ng/mL, with accuracy ranging from 1% to 27% and precision (% R.S.D.) ranging from 2% to 10% between the lower and upper limits of quantitation for the analysis of 7-aminoflunitrazepam in urine. The dynamic range of the method is from 0.02 ng/mL, which is limited by the instrument sensitivity, to 0.5 ng/mL, which is approaching the capacity of the probes. This would allow for quantitative analysis of samples at concentrations below that measurable by many other methods for general benzodiazepines analysis from urine, and a highly selective screen for samples at higher concentrations. The method has similar limits of detection to the most sensitive literature methods specifically designed for such analysis but with the advantage of significantly simplified sample preparation. This simplification makes the technique more amenable for use by both professionals and non-professionals.

A surface modification strategy on silicon nitride for developing biosensors

A surface modification strategy for the use of giant magnetoresistive materials in the detection of protein-protein interactions is developed. This modification strategy is based on silanization of semiconductive materials. A native silicon nitride surface was treated with concentrated hydrofluoric acid to improve surface homogeneity. Nano-strip was used to oxidize silicon nitride to form a hydrophilic layer. Aminopropyltriethoxysilane was subsequently used to functionalize the treated surfaces to form amine groups, which were further activated with glutaraldehyde to introduce a layer of aldehyde groups. The effectiveness of this modification strategy was validated by chemiluminescence immunoassays of purified 6x His-HrpW of Pseudomonas syringae pv. tomato DC3000 and human transferrin. Signals with intensities related to concentrations of these two immobilized model proteins were observed. The modified surface was also validated by a more complex system: intercellular proteins secreted by DC3000. HrpW in these protein mixtures was successfully recognized by anti-HrpW antibodies when mixed proteins were immobilized onto activated surfaces. This surface modification strategy provides a platform onto which proteins can be directly immobilized for biosensor and protein array applications.

Monitoring bronchodilators with direct injection

A procedure was developed for the determination of caffeine and theophylline using a C18 column (5 microm, 250 mm x 4.6 mm) and micellar liquid chromatography using hybrid mobile phases containing sodium dodecyl sulfate (SDS) and propanol, butanol or pentanol as modifiers. Detection was performed with a variable wavelength UV-vis detector at 272 nm. After the application of an interpretative strategy for the selection of the optimimum mobile phase, caffeine and theophylline can be resolved and determined in serum samples by direct injection, using a mobile phase made up of 50 mM SDS-2.5% (v/v) propanol-10 mM KH2PO4, pH 7, with an analysis time below 5 min. Calibration was linear in the range 0.05 to 50 microg mL(-1) with r > 0.999. The statistical evaluation of the method was examined by performing intra-day (n = 6) and inter-day calibration (n = 7) and was found to be satisfactory, with highly accurate and precise results. The proposed method was suitably validated and applied to the determination of caffeine and theophylline in serum samples of patients treated with bronchodilators.

Study of Ligand−Receptor Binding Using SPME: Investigation of Receptor, Free, and Total Ligand Concentrations

The theoretical background and practical approaches for studying ligand-receptor (protein) binding by solid phase microextraction (SPME) are investigated, along with methods for simultaneous calculation of receptor, free, and total ligand concentrations. With the introduction of new extraction phases (restricted access materials, molecularly imprinted polymers, and immobilized antibodies), SPME allows better separation of small molecules of ligand from larger molecules of receptor, and improved accuracy. This sample preparation method based on nonexhaustive extraction is well suited as a general method to study and quantify systems involving multiple equilibriums, with significant advantages over currently used methods. SPME was used previously for the determination of protein binding constants, but only with conventional extraction phases and in simple cases, with a 1:1 combination ratio between the ligand and the receptor or when negligible depletion conditions were met. The new theoretical approach presented in this study allows the quantification of any binding equilibrium, regardless of the extent of depletion. Restricted-access particles are used as extraction phase, and if the amount of receptor is limited, selected regions of the binding curve may be obtained using a single sample, with a volume as low as 10 muL. The equations developed here are simple and independent of the analytical method used for the quantification of the amount of ligand. Three different practical approaches are presented: the method of multiple standard solutions, the method of successive extractions from the same sample and the method of successive additions to the same sample. The usefulness of this novel approach is demonstrated by using it to determine the binding parameters of some selected drugs to human serum albumin. These parameters are subsequently used to calculate albumin, free drug, and total drug concentrations from unknown mixtures. The results are in good agreement with previously published data. Quantification of the amount of ligand extracted by SPME is done by liquid chromatography coupled with tandem mass spectrometry.

Preparation and characterization of polydimethylsiloxane/poly(vinylalcohol) coated solid phase microextraction fibers using sol–gel technology

The applicability of a composite composed of polydimethylsiloxane (PDMS) and poly(vinyl alcohol) (PDMS/PVA) as coating sorbent for SPME fibers is demonstrated here. Fused silica (FS) fibers were coated with PDMS/PVA composite through a sol-gel process, using methyltrimethoxysilane as reticulating agent. The chemical and physical properties of the sol-gel PDMS/PVA composite were determined by infrared spectroscopy and thermogravimetric analysis. Electron scanning microscopy of the prepared fibers, showed that the coating obtained was highly microporous, having a thickness of approximately 5 microm. The fibers were tested for the headspace extraction of several organic compounds (o-xylene, naphthalene, ethyl caprate, p-chlorotoluene and PCB) prior to gas chromatographic analysis. The extractive capacity of the PDMS/PVA coating was found to be superior to that of pure conventional PDMS fibers.

Silicon surface modification with a mixed silanes layer to immobilize proteins for biosensor with imaging ellipsometry

One kind of surface modification method on silicon wafer was presented in this paper. A mixed silanes layer was used to modify silicon surface and rendered the surface medium hydrophobic. The mixed silanes layer contained two kinds of compounds, aminopropyltriethoxysilane (APTES) and methyltriethoxysilane (MTES). A few of APTES molecules in the layer was used to immobilize covalently human immunoglobulin G (IgG) on the silicon surface. The human IgG molecules immobilized covalently on the modified surface could retain their structures well and bind more antibody molecules than that on silicon surface modified with only APTES. This kind of surface modification method effectively improved the sensitivity of the biosensor with imaging ellipsometry.