Design and fabrication of biochemical sensors: Innovative materials that enhance electrochemical transduction

Projected increases in pollutants and waste products warrants the need for biochemical sensor–based monitoring technologies for efficient protection, remediation, and restoration of the environment, and also addresses the issue of homeland security. Efforts to develop biochemical sensors for environmental monitoring in projects funded by the Malaysia Ministry of Education (MOE) under the fundamental/basic grants and by private awards such as the L'Oréal-UNESCO award for applied research will be presented. Work has been done to optimize the electrochemical transducer layer of biochemical sensors in terms of stability, sensitivity, detection limit, and mechanical properties utilizing conductive polymers and/or graphene-based nanomaterial composites. Results show that electrochemical deposition of ethylene dioxythiophene (EDOT) and its conjugates as transducer layers can retain redox capability over multiple sensor use and provide stable current measurements in a water-flow test. Furthermore, Fourier transform infrared spectroscopy (FTIR) results reveal that methods of graphene oxide reduction affect sensor performance in terms of sensitivity and detection limit owing to the availability of surface functional groups. Biochemical sensors have been developed to successfully detect and quantify E. coli O157:H7 and ions involved in water-quality monitoring; the sensors are currently being integrated with portable platforms such as open-source microprocessors intended for field-work use

Electrochemical sensor centrifuge platform for single-cell study

SporeSat – a lab-on-a-chip (LOC) centrifuge platform designed for integration as the payload of a small (5.5 kg), free-flying satellite – has been developed to determine the gravitational thresholds for calcium-ion channel activation of a single-cell spore from the fern Ceratopteris richardii. This fern is an important model system for gravity-directed plant-cell development during variable-gravity conditions attainable only in space flight. Calcium-ion channel activity is measured by photolithographically defined calcium ion–selective electrodes (ISEs) at opposite ends of each spore. Artificial gravity is created by rotating a disk-like platform that contains the spores in wells along with the calcium ISEs. Ground experiments reveal a maximum calcium concentration ratio at 2.2xg, between micro-ion-selective electrodes near the “top” and “bottom” ends of the spore, indicating an increasing calcium concentration at one “end” of the fern spore with respect to the other. Confocal micrographs of rhizoid formation confirm the light-induced germination. SporeSat is a spaceflight experiment that will take ~ 4 days; data will be telemetered to Earth over ~ 100 days

Reduced graphene oxide on screen-printed carbon electrodes as biosensor for Escherichia coli O157:H7 detection

Rapid development and deployment of biosensors for pathogen quantification is needed for flood-stricken areas. Drinking-water supplies in flooded areas become a disease threat owing to mixture with sewage discharge. In such exigent conditions, water is filtered through a microfiltration technique that is moderately effective in removing bacteria and non-effective in removing viruses. Quantification of pathogens using biochemical techniques does not provide real-time data and requires transportation of water samples to laboratories for analysis. However, transportation services are severely affected during flooding, and hence on-site testing may be the only option. WHO specifies that diagnostic devices are to be made ASSURED – affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free, and deliverable to end-users. To fulfil ASSURED criteria, we developed a low-cost electrochemical biosensor integrated with an Arduino® microprocessor encased in a portable platform for E. coli O157:H7 quantification. The working electrode (WE) of a screen-printed carbon electrode (SPCE) was modified with reduced graphene oxide (rGO). Rabbit serum IgG, a non-specific antibody towards E. coli O157:H7, was immobilized on the WE. We tested the specificity of E. coli O157:H7 binding to IgG/rGO/SPCEs and rGO/SPCEs at 4 to 4 × 108 CFU/ml. We chose a potential range of -0.35 to 0.07 in LSV to compare the current values at different concentrations. At -0.14V, IgG/rGO/SPCEs distinguished E. coli concentrations of 4 and 4 × 108 CFU/ml with current value of 17 µA and 1 µA, respectively. However, the IgG/rGO/SPCE does not distinguish between E. coli concentration of 4 × 107 and 4 × 108 CFU/ml. The rGO/SPCE does not distinguish E. coli concentration of 4 and 4 × 108 CFU/ml, as evidenced by almost similar current values in both concentrations. This study indicates the potential of non-specific antibodies for E. coli O157:H7 quantification during water-quality monitoring in flooded areas

Characterization of enzymatic glucose biosensor in buffer solution, in artificial saliva, and in potassium ferricyanide by linear sweep voltammetry

Existing practice of glucose-level monitoring for diabetic patients involves frequent finger pricking for blood samples. This is not only constantly painful, but could make patients susceptible to infections. A non-invasive, portable, graphene-based biosensor is being developed to measure glucose levels in saliva instead of in blood, by incorporating rGO-PEDOT:PSS composites as the transducer layer on a working electrode – a screen-printed carbon electrode (SPCE) 2 mm in diameter. To evaluate the performance of the biosensor, the electrochemical technique of linear sweep voltammetry (LSV) was used. The results showed sensitivity of rGO-PEDOT:PSS-GOx/SPCE in artificial saliva: 105 μA/mM (σ = 12.52) at no glucose to 0.2 mM glucose concentrations and 35.33 μA/mM (σ = 5.79) at glucose concentrations of 0.2 mM to 0.6 mM, with correlation coefficient of 0.99. The sensitivity of the biosensor in 10 mM PBS (pH 6.8) is 9.88 μA/mM (σ = 2.74), while in 100 mM potassium ferricyanide it is 10.48 μA/mM (σ = 0.49). The high sensitivity obtained in artificial saliva suggests that the rGO-PEDOT:PSS composite is suitable for use as a transducer layer for non-invasive glucose monitoring

Enzyme-based biosensors for electrochemical detection of pesticides - a mini review

Despite their important contribution in increasing crops production, most pesticides are harmful to humans and living beings and can persist in the environment over long a long duration. Traditional chromatographic methods of analysis are expensive and cumbersome. Biosensor technology appears therefore as an efficient and economical alternative for fast detection of pesticides. The devices are portable, rapid, and highly sensitive. Other important features of the devices are their relatively high sensistivity and low response time. Enzymatic biosensors for pesticide detection rely either on the inhibition mechanism or on the catalytic activity of the immobilized enzyme toward a specific pesticide. Metal and carbon based nanomaterials are being widely used as immobilization support owing to novel characteristics such as biocompatibility and enhanced electron transfer ability for sensitive electrochemical detection, among others. This review focusses on the electrochemical detection of organophosphorus pesticides, delineating the limit of detection and response time of biosensors toward a wide range of organophosphorus pesticides

Battery characterization of hybrid car

In this paper, batteries are characterized in order to propose a better monitoring and to maximize the energy outputs of the hybrid car. The characteristics of the batteries are compared between two types of the batteries, which is a lead-acid battery, and lithium-ion polymer battery. A simulation model by software COMSOL TM Multiphysics is conducted to simulate the characteristic of the electrochemistry of the batteries and to calculate the voltage drawn as well as the polarization in order to find the optimum characteristics for the hybrid car. For both batteries, the outcomes are voltage drops, state-of-charge (SOC), discharge rate, and the rate of capability. Simulation results indicate that lithium-ion polymer has a higher specific energy and specific density that hybrid car needed compared to the lead-acid battery

Tailoring the electrochemical and morphological properties of electropolymerized and Dropcast rGO:PSS-PEDOT:PSS transducers for ion-selective sensors

Fabrication of ion-selective sensors for continuous measurement in fluids depends on understanding the electrochemical and morphological properties of transducers. Electropolymerized nanomaterials essentially offer stable transducers that can reduce measurement drifts. This study aims to elucidate the electrochemical and morphological characteristics of electropolymerized reduced graphene oxide stabilized in polystyrenesulfonate and poly(3,4-ethylenedioxythiophene): polystyrenesulfonate composites on screen-printed carbon electrodes (rGO:PSS-PEDOT:PSS/SPCEs) using scanning electron microscopy (SEM) and cyclic voltammetry (CV) in 0.1 M ferricyanide (Fe(CN)64/3-). We fabricated the rGO:PSS-PEDOT:PSS/SPCEs by two different techniques: electropolymerization deposition (EPD) and drop-casting (DC). Results revealed smaller peak-to-peak potential separation (ΔEp) of 360 mV for EPD rGO:PSS-PEDOT:PSS/SPCEs, compared to 510 mV for the DC rGO:PSS-PEDOT:PSS/SPCEs. A smaller ΔEp indicates higher reversibility and faster electron-transfer rate at the electrode-analyte interface. SEM results showed EPD rGO:PSS-PEDOT:PSS/SPCEs have the roughest surface among electrodes; homogeneous globular structures with diameter range of 1.4–5.3 μm covered the electrode surface. In terms of electrode integrity in fluids, cracks can be seen on the surface of DC PEDOT:PSS/SPCEs after undergoing CV in 0.1 M Fe(CN)64/3-, whereas rGO:PSS-PEDOT:PSS/SPCEs for both deposition methods maintained their integrity. Globular structures of rGO:PSS-PEDOT:PSS using EPD methods remained after undergoing CV. The results suggest that EPD serves as a potential method to fabricate a stable transducer for ion-selective sensing. This study aims to elucidate performance of nanocomposites via EPD methods, to develop stable ion-selective sensors for physiological and environmental applications

Cyclic voltammetry and electrochemical impedance spectroscopy of partially reduced graphene oxide - PEDOT:PSS transducer for biochemical sensing

Electron-transfer kinetics and impedance at the electrode-solution interface affect biosensor performance. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy(EIS) are used to understand the reversibility of electron transfer and impedance at the electrode-solution interface, respectively. Effective surface areas calculated based on the Randles-Sevcik equation for a bare screen-printed carbon electrode (SPCE), a graphene oxide (GO)-poly (3,4-ethylenedioxythiophene):polystyrenesulfonic acid (PEDOT:PSS)–modified electrode (GO-PEDOT:PSS/SPCE), a partially reduced graphene oxide-PEDOT:PSS–modified electrode (prGO-PEDOT:PSS/SPCE), and glucose oxidase (GOx) crosslinked with glutaraldehyde on partially reduced graphene oxide-PEDOT:PSS–modified electrodes (GOx/prGOPEDOT:PSS/SPCE) are 0.0717 mm2, 0.0794 mm2, 0.219 mm2, and 0.160 mm2, respectively. Nyquist plots from EIS show charge transfer resistance (Rct) of 430 μΩ, 148.2 Ω, 200.7 Ω, and 209.6 Ω, respectively, for the same electrodes. The high effective surface area and the Rct of prGO-PEDOT:PSS/SPCE indicate that the prGO-PEDOT:PSS composite is suitable as a transducer layer for glucose biosensing

ELECTROCHEMICAL CHARACTERIZATION OF POLYLACTIC ACID-BLOCK-POLY(2-VINYLPYRIDINE)/GOLD NANOPARTICLE COMPOSITES FOR GLUCOSE BIOSENSOR DEVELOPMENT

Nanocomposites that consist of diblock copolymer (BCP) and gold nanoparticles (AuNPs) can be applied as a matrix to immobilize enzymes or other molecules based on the well-defined core/shell nanostructures of these composites. In this research, polylactic acid-block-poly(2-vinylpyridine) (PLA-b-P2VP)/hydrogen tetrachloroaurate(III) hydrate (HAuCl4.3H2O) composites were hybridized and then reduced in dichloromethane (DCM) solution. The hybridizations between gold precursors and the P2VP domain were prepared with different ratios of gold to P2VP block (1:1, 1:5, 1:10, 5:1, 10:1) by taking advantage of the association between the long-pair nitrogen of the pyridine group of P2VP. The reduction of the Au3+/PLA-b-P2VP composite was accomplished by hydrazine solution in order to get gold nanoparticle/PLA-b-P2VP composites, which was visually confirmed by a direct color change from bright yellow to purple. In this work, ultraviolet–visible (UV-vis) spectroscopy and Fourier transform infrared spectroscopy (FTIR) were used to confirm the association between gold precursors and pyridine groups as well as the synthesis of gold nanoparticles.The composite which labeled as R3 (Au3+: P2VP = 10:1) showed the highest peak current based on the cyclic voltammetry (CV) measurment. Furthermore, graphene oxide (GO) was added into R3 to prepare BCP/AuNPs/GO composite and reduced to BCP/AuNPs/rGO through electrochemical reduction. The resulting BCP/AuNPs/rGO showed high potential to be used in amperometric biosensor

Low-cost microcontact printing for direct enzyme patterning on paper

In this study, an easy, low-cost, and straightforward method to pattern and directly control the amount of enzyme deposited on paper using microcontact printing was successfully developed without the need for a cleanroom facility. Full characterization was done to evaluate the effectiveness of this approach, from the fabrication of a master stamp with controlled width spacing of 20, 50, and 100 μm using a vertical micromilling method to the stamping of glucose oxidase (GOx) onto papers with different porosity. To prove the concept of direct enzyme patterning, GOx is patterned on paper impregnated with anthocyanin, a water-soluble vacuolar pigment. Anthocyanin contains glucose covalently attached to the flavonoid backbone and is able to give a colorimetric change from purple to red to indicate successful deposition of GOx owing to the product of gluconic acid. Stamping process parameters were varied in terms of force (8, 20, 40, and 50 g) and time (5, 30, and 60 s) to transfer GOx from soft stamp to porous paper. Results show that the paper with the highest porosity stamped using a 200 g load for 5 s, gives the best result in terms of patterns and successful transfer of enzyme onto the paper. This study suggests that the fabrication of a master stamp using inexpensive micromilling methods can produce a soft stamper that can pattern a bioactive enzyme