Tungsten Disulfide Nanotube-Modified Conductive Paper-Based Chemiresistive Sensor for the Application in Volatile Organic Compounds' Detection.

Toxic and nontoxic volatile organic compound (VOC) gases are emitted into the atmosphere from certain solids and liquids as a consequence of wastage and some common daily activities. Inhalation of toxic VOCs has an adverse effect on human health, so it is necessary to monitor their concentration in the atmosphere. In this work, we report on the fabrication of inorganic nanotube (INT)-tungsten disulfide, paper-based graphene-PEDOT:PSS sheet and WS2 nanotube-modified conductive paper-based chemiresistors for VOC gas sensing. The WS2 nanotubes were fabricated by a two-step reaction, that is oxide reduction and sulfurization, carried out at 900 °C. The synthesized nanotubes were characterized by FE-SEM, EDS, XRD, Raman spectroscopy, and TEM. The synthesized nanotubes were 206-267 nm in diameter. The FE-SEM results show the length of the nanotubes to be 4.5-8 µm. The graphene-PEDOT:PSS hybrid conductive paper sheet was fabricated by a continuous coating process. Then, WS2 nanotubes were drop-cast onto conductive paper for fabrication of the chemiresistors. The feasibility and sensitivity of the WS2 nanotube-modified paper-based chemiresistor were tested in four VOC gases at different concentrations at room temperature (RT). Experimental results show the proposed sensor to be more sensitive to butanol gas when the concentration ranges from 50 to 1000 ppm. The limit of detection (LOD) of this chemiresistor for butanol gas was 44.92 ppm. The WS2 nanotube-modified paper-based chemiresistor exhibits good potential as a VOC sensor with the advantages of flexibility, easy fabrication, and low fabrication cost.

A Graphene-PEDOT:PSS Modified Paper-Based Aptasensor for Electrochemical Impedance Spectroscopy Detection of Tumor Marker.

A graphene and poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) modified conductive paper-based electrochemical impedance spectroscopy (EIS) aptasensor has been successfully fabricated by a simple and continuous coating process. A graphene/PEDOT:PSS modified paper electrode forms the nanocomposite providing a conductive and sensitive substrate for further aptamer functionalization of the biosensor. This low-cost paper-based aptasensor exhibits its sensitivity to carcinoembryonic antigens (CEA) in standard buffer solutions and human serum samples in a linear range of 0.77-14 ng·mL-1. The limit of detection (LOD) is found to be 0.45 ng·mL-1 and 1.06 ng·mL-1 for CEA in both samples, separately. This aptamer-based sensing device was also evaluated and received a good correlation with the immunoassay detection method. The proposed paper-based aptasensor has demonstrated its potential as a rapid simple point-of-care analytical platform for early cancer diagnosis in less developed areas where manufacturing facilities, analytical instruments, and trained specialists are limited.

Easy and Fast Western Blotting by Thin-Film Direct Coating with Suction.

Thin-film direct coating (TDC) has been successfully used in Western blotting (WB). In this study, the advanced technique of TDC with suction (TDCS) was developed to reduce the consumption amount of antibody by a factor of up to 10(4) in comparison with the amount consumed by the conventional WB using the capillary tube without any need of special micromachining processes. The operation time for completely finishing a high-quality WB can be reduced from 3 h in conventional WB to about 5 min or even less by TDCS. In addition, the signal-to-noise ratio of the immunoblotting by TDCS can be markedly increased. TDCS WB showed a high linearity within a 6-log2 dynamic range for detecting 90-6000 ng of purified recombinant glutathione-S-transferase (GST) proteins and could particularly detect extrinsic GST proteins added in crude Escherichia coli or 293T cell lysates. Moreover, a protein mixture containing bovine serum albumin, GST, and ubiquitin could be specifically probed in parallel with their corresponding antibodies through multichannel TDCS WB. This simple and innovative TDCS WB offers various potential applications in simultaneously finishing multiple antibody-antigen screenings in a fast and single experiment.

Western blotting by thin-film direct coating.

A novel thin-film direct coating (TDC) technique was developed to markedly reduce the amount of antibody required for Western blotting (WB). Automatic application of the technique for a few seconds easily and homogeneously coats the specific primary antibody on the polyvinylidene fluoride (PVDF) membrane. While conventional WB requires 0.4 µg of the primary antibody, the proposed technique only uses 4 × 10(-2) µg, which can be reduced further to 4 × 10(-5) µg by reducing the coater width. Moreover, the proposed process reduces antibody probing times from 60 to 10 min. The quantification capability of TDC WB showed high linearity within a 4-log2 dynamic range for detecting target antigen glutathione-S-transferase. Furthermore, TDC WB can specifically detect the extrinsic glutathione-S-transferase added in the Escherichia coli or 293T cell lysate with better staining sensitivity than conventional WB. TDC WB can also clearly probe the intrinsic ß-actin, α-tubulin, and glyceraldehyde 3-phosphate dehydrogenase, which are usually used as control proteins in biological experiments. This novel technique has been shown to not only have valuable potential for increasing WB efficiency but also for providing significant material savings for future biomedical applications.

Electrical detection of C-reactive protein using a single free-standing, thermally controlled piezoresistive microcantilever for highly reproducible and accurate measurements.

This study demonstrates a novel method for electrical detection of C-reactive protein (CRP) as a means of identifying an infection in the body, or as a cardiovascular disease risk assay. The method uses a single free-standing, thermally controlled piezoresistive microcantilever biosensor. In a commonly used sensing arrangement of conventional dual cantilevers in the Wheatstone bridge circuit, reference and gold-coated sensing cantilevers that inherently have heterogeneous surface materials and different multilayer structures may yield independent responses to the liquid environmental changes of chemical substances, flow field and temperature, leading to unwanted signal disturbance for biosensing targets. In this study, the single free-standing microcantilever for biosensing applications is employed to resolve the dual-beam problem of individual responses in chemical solutions and, in a thermally controlled system, to maintain its sensor performance due to the sensitive temperature effect. With this type of single temperature-controlled microcantilever sensor, the electrical detection of various CRP concentrations from 1 µg/mL to 200 µg/mL was performed, which covers the clinically relevant range. Induced surface stresses were measured at between 0.25 N/m and 3.4 N/m with high reproducibility. Moreover, the binding affinity (KD) of CRP and anti-CRP interaction was found to be 18.83 ± 2.99 µg/mL, which agreed with results in previous reported studies. This biosensing technique thus proves valuable in detecting inflammation, and in cardiovascular disease risk assays.

Laser-scribed Graphene Electrodes Functionalized with Nafion/Fe3O4 Nanohybrids for the Ultrasensitive Detection of Neurotoxin Drug Clioquinol.

The analysis of pharmaceutical active ingredients plays an important role in quality control and clinical trials because they have a significant physiological effect on the human body even at low concentrations. Herein, a flexible three-electrode system using laser-scribed graphene (LSG) technology, which consists of Nafion/Fe3O4 nanohybrids immobilized on LSG as the working electrode and LSG counter and reference electrodes on a single polyimide film, is presented. A Nafion/Fe3O4/LSG electrode is constructed by drop coating a solution of Nafion/Fe3O4, which is electrostatically self-assembled between positively charged Fe3O4 and negatively charged Nafion on the LSG electrode and is used for the first time to determine a neurotoxicity drug (clioquinol; CQL) in biological samples. Owing to their porous 3D structure, an enriched surface area at the active edges and polar groups (OH, COOH, and -SO3H) in Nafion/Fe3O4/LSG electrodes resulted in excellent wettability to facilitate electrolyte diffusion, which gave ∼twofold enhancement in electrocatalytic activity over LSG electrodes. The experimental parameters affecting the analytical performance were investigated. The quantification of clioquinol on the Nafion/Fe3O4/LSG electrode surface was examined using differential pulse voltammetry and chronoamperometry techniques. The fabricated sensor displays preferable sensitivity (17.4 µA µM-1 cm-2), a wide linear range (1 nM to 100 µM), a very low detection limit (0.73 nM), and acceptable selectivity toward quantitative analysis of CQL. Furthermore, the reliability of the sensor was checked by CQL detection in spiked human blood serum and urine samples, and satisfactory recoveries were obtained.

Portable Real-Time Detection of Pb(II) Using a CMOS MEMS-Based Nanomechanical Sensing Array Modified with PEDOT:PSS.

Detecting the concentration of Pb2+ ions is important for monitoring the quality of water due to it can become a health threat as being in certain level. In this study, we report a nanomechanical Pb2+ sensor by employing the complementary metal-oxide-semiconductor microelectromechanical system (CMOS MEMS)-based piezoresistive microcantilevers coated with PEDOT:PSS sensing layers. Upon reaction with Pb2+, the PEDOT:PSS layer was oxidized which induced the surface stress change resulted in a subsequent bending of the microcantilever with the signal response of relative resistance change. This sensing platform has the advantages of being mass-produced, miniaturized, and portable. The sensor exhibited its sensitivity to Pb2+ concentrations in a linear range of 0.01-1000 ppm, and the limit of detection was 5 ppb. Moreover, the sensor showed the specificity to Pb2+, required a small sample volume and was easy to operate. Therefore, the proposed analytical method described here may be a sensitive, cost-effective and portable sensing tool for on-site water quality measurement and pollution detection.

A CMOS MEMS-based Membrane-Bridge Nanomechanical Sensor for Small Molecule Detection.

Small molecule compounds are necessary to detect with high sensitivity since they may cause a strong effect on the human body even in small concentrations. But existing methods used to evaluate small molecules in blood are inconvenient, costly, time-consuming, and do not allow for portable usage. In response to these shortcomings, we introduce a complementary metal-oxide-semiconductor bio-microelectromechanical system (CMOS BioMEMS) based piezoresistive membrane-bridge (MB) sensor for detecting small molecule (phenytoin) concentrations as the demonstration. Phenytoin is one of anticonvulsant drugs licensed for the management of seizures, which has a narrow therapeutic window hence a level of concentration monitoring was needed. The MB sensor was designed to enhance the structural stability and increase the sensitivity, which its signal response increased 2-fold higher than that of the microcantilever-based sensor. The MB sensor was used to detect phenytoin in different concentrations from 5 to 100 µg/mL. The limit of detection of the sensor was 4.06 ± 0.15 µg/mL and the linear detection range was 5-100 µg/mL, which was within the therapeutic range of phenytoin concentration (10-20 µg/mL). Furthermore, the MB sensor was integrated with an on-chip thermal effect eliminating modus and a reaction tank on a compact chip carrier for disposable utilization. The required amount of sample solution was only 10 µL and the response time of the sensor was about 25 minutes. The nano-mechanical MB sensing method with thermal effect compensation is specific, sensitive, robust, affordable and well reproducible; it is, therefore, an appropriate candidate for detecting small molecules.

Portable Nanohybrid Paper-Based Chemiresistive Sensor for Free Chlorine Detection.

Detecting the concentration of free chlorine is important for monitoring the quality of water. In this study, we report a nanohybrid paper-based chemiresistive sensor that can be used with smartphones to detect free chlorine ions. The sensor was fabricated using a simple and standardized coating process. The graphene and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) nanohybrid paper-based sensing device exhibited a more stable and intuitive response to free chlorine than that exhibited by the device using only PEDOT:PSS. The nanohybrid paper-based sensor was sensitive to free chlorine concentrations in a linear range of 0.1-500 ppm, and the limit of detection was 0.18 ppm. The sensor showed specificity for free chloride ions and detection capability in samples. The sensor was integrated as a module with an electric readout system, and the measured signals and results could be displayed in real time on a smartphone. Therefore, the proposed sensing platform is suitable owing to its portability, low cost, ease of use, and capability for on-site water quality measurement.

Gentamicin drug monitoring for peritonitis patients by using a CMOS-BioMEMS-based microcantilever sensor.

We developed a Complementary Metal-Oxide-Semiconductor Bio-Microelectromechanical Systems (CMOS-BioMEMS) based piezoresistive microcantilever sensor for detecting gentamicin, a peritonitis therapeutic small-molecule drug. In recent years, the patient-centric concept has been emphasized. In such a trend, therapeutic drug monitoring (TDM) is especially crucial for patients with peritonitis to avoid adverse reactions from a high concentration of gentamicin in the blood. With the aid of a commercialized semiconductor manufacturing process, the microcantilever sensing platform can serve as a portable, low-cost device and offer real-time detection. With chemical surface modification and capture antibody immobilization, the sensor can detect the small-molecule (< 2 kDa) gentamicin directly. We also modified the pH value of the buffer solution and applied an external electric field to promote sensor sensitivity. Comparing the change of the signals in a non-electric field of antibody immobilization and a 60-volt electric field of antibody immobilization showed that the average signal response increased 1.8 times. In the detection of gentamicin with different concentrations of 10-200 µg/mL, the limit of detection (LOD) of the sensor was 9.44 µg/mL. Finally, the detecting result of a microrcantilever sensor was compared with the one measured by a common instrument in hospital, and the high correlation was expressed between them in gentamicin detection. The CMOS-BioMEMS-based piezoresistive microcantilever sensor has been demonstrated to have great potential as a point-of-care (POC) device for real-time drug concentration monitoring.

A Real-Time Thermal Self-Elimination Method for Static Mode Operated Freestanding Piezoresistive Microcantilever-Based Biosensors.

Here, we provide a method and apparatus for real-time compensation of the thermal effect of single free-standing piezoresistive microcantilever-based biosensors. The sensor chip contained an on-chip fixed piezoresistor that served as a temperature sensor, and a multilayer microcantilever with an embedded piezoresistor served as a biomolecular sensor. This method employed the calibrated relationship between the resistance and the temperature of piezoresistors to eliminate the thermal effect on the sensor, including the temperature coefficient of resistance (TCR) and bimorph effect. From experimental results, the method was verified to reduce the signal of thermal effect from 25.6 µV/°C to 0.3 µV/°C, which was approximately two orders of magnitude less than that before the processing of the thermal elimination method. Furthermore, the proposed approach and system successfully demonstrated its effective real-time thermal self-elimination on biomolecular detection without any thermostat device to control the environmental temperature. This method realizes the miniaturization of an overall measurement system of the sensor, which can be used to develop portable medical devices and microarray analysis platforms.

Direct determination of a small-molecule drug, valproic Acid, by an electrically-detected microcantilever biosensor for personalized diagnostics.

Direct, small-molecule determination of the antiepileptic drug, valproic acid, was investigated by a label-free, nanomechanical biosensor. Valproic acid has long been used as an antiepileptic medication, which is administered through therapeutic drug monitoring and has a narrow therapeutic dosage range of 50-100 µg·mL-1 in blood or serum. Unlike labeled and clinically-used measurement techniques, the label-free, electrical detection microcantilever biosensor can be miniaturized and simplified for use in portable or hand-held point-of-care platforms or personal diagnostic tools. A micromachined microcantilever sensor was packaged into the micro-channel of a fluidic system. The measurement of the antiepileptic drug, valproic acid, in phosphate-buffered saline and serum used a single free-standing, piezoresistive microcantilever biosensor in a thermally-controlled system. The measured surface stresses showed a profile over a concentration range of 50-500 µg·mL-1, which covered the clinically therapeutic range of 50-100 µg·mL-1. The estimated limit of detection (LOD) was calculated to be 45 µg·mL-1, and the binding affinity between the drug and the antibody was measured at around 90 ± 21 µg·mL-1. Lastly, the results of the proposed device showed a similar profile in valproic acid drug detection with those of the clinically-used fluorescence polarization immunoassay.

Detection of the antiepileptic drug phenytoin using a single free-standing piezoresistive microcantilever for therapeutic drug monitoring.

Phenytoin, one of the most widely used antiepileptic drugs, suppresses the abnormal brain activity often seen in seizures. In this study, we report the electrical detection of phenytoin as an antiepileptic medication with a narrow therapeutic dosage range to which therapeutic drug monitoring (TDM) is applied. The measurement technique used an electrical detection of a piezoresistive microcantilever biosensor. This label-free, electrically measured microcantilever can be miniaturized in order to be portable for point-of-care, personal diagnosis or for personalized therapeutic drug monitoring. The miniaturized piezoresistive microcantilever was fabricated by micro-electro-mechanical system processes, and was integrated into a microfluidic channel with a system for label-free detection. The microcantilever biosensor was approved for the detection of phenytoin in solutions of deionized water and 100% fetal bovine serum. A linear profile in a drug-concentration range of 10-80 µg/mL was detected, with the signal resolution being about 0.005 Ω. The concentration sensitivity was 2.94×10(-6) (µg/mL)(-1). The binding affinity (KD) was calculated to be 58 µg/mL. The results of the present piezoresistive microcantilever biosensors showed a solid correlation of phenytoin drug detection with that in the clinically used fluorescence polarization immunoassay (FPIA).