Electrochemical biosensor based on microfabricated electrode arrays for life sciences applications

In developing a biosensor, the utmost important aspects that need to be emphasized are the specificity and selectivity of the transducer. These two vital prerequisites are of paramount in ensuring a robust and reliable biosensor. Improvements in electrochemical sensors can be achieved by using microelectrodes and to modify the electrode surface (using chemical or biological recognition layers to improve the sensitivity and selectivity). The fabrication and characterisations of silicon-based and glass-based gold microelectrode arrays with various geometries (band and disc) and dimension (ranging from 10 μm-100 nm) were reported. It was found that silicon-based transducers of 10 μm gold microelectrode array exhibited the most stable and reproducible electrochemical measurements hence this dimension was selected for further study. Chemical electrodeposition on both 10 μm microband and microdisc were found viable by electro-assisted self-assembled sol-gel silica film and nanoporous-gold electrodeposition respectively. The fabrication and characterisations of on-chip electrochemical cell was also reported with a fixed diameter/width dimension and interspacing variation. With this regard, the 10 μm microelectrode array with interspacing distance of 100 μm exhibited the best electrochemical response. Surface functionalisations on single chip of planar gold macroelectrodes were also studied for the immobilisation of histidine-tagged protein and antibody. Imaging techniques such as atomic force microscopy, fluorescent microscopy or scanning electron microscope were employed to complement the electrochemical characterisations. The long-chain thiol of self-assembled monolayer with NTA-metal ligand coordination was selected for the histidine-tagged protein while silanisation technique was selected for the antibody immobilisation. The final part of the thesis described the development of a T-2 labelless immunosensor using impedimetric approach. Good antibody calibration curve was obtained for both 10 μm microband and 10 μm microdisc array. For the establishment of the T-2/HT-2 toxin calibration curve, it was found that larger microdisc array dimension was required to produce better calibration curve. The calibration curves established in buffer solution show that the microelectrode arrays were sensitive and able to detect levels of T-2/HT-2 toxin as low as 25 ppb (25 μg kg-1) with a limit of quantitation of 4.89 ppb for a 10 μm microband array and 1.53 ppb for the 40 μm microdisc array

Flight intensity of two species of stingless bees Heterotrigona itama and Geniotrigona thoracica and its relationships with temperature, light intensity and relative humidity

Information on flight intensity of stingless bees is important in pollinator management programs. However, the flight intensity of local stingless bees especially for Heterotrigona itama and Geniotrigona thoracica is poorly known. Investigations into the pattern of activity of various species of meliponinae, in different parts of the world, reveal a lot of variations. Hence, this study was designated to determine the effect of daytime and climatic factors on the flight of stingless bees. This study was conducted at Orchad 10, Universiti Putra Malaysia, Serdang, Selangor and the flight intensity of bees was determined by counting the numbers of bees leaving and returning to their nest for ten minutes observations. Counting was done in six colonies which had similar strength. It was done five times per day at 8.00 am, 10.00 am, 12.00 pm, 2.00 pm and 4.00 pm for six days. The peak number of bees that exited and returned was recorded around 8.00 am to 10.00 am for both species. The number of Geniotrigona thoracica exited from the entrance had a positive correlated to air temperature, relative humidity and light intensity. Meanwhile for Heterotrigona itama, their flight activities were affected by temperature and light intensity. Hence it is advisable to save stingless bees by not applying insecticide to crops at times of day when their flight intensity is highest

Fabrication and characterization of microfabricated on-chip microelectrochemical cell for biosensing applications

The fabrication of on-chip microelectrochemical cell on Si wafer by means of photolithography is described here. The single on-chip microelectrochemical cell device has dimensions of 100 × 380 mm with integrated Pt counter electrode (CE), Ag/AgCl reference electrode (RE) and gold microelectrode array of 500 nm recess depth as the working electrode (WE). Two geometries of electrode array were implemented, band and disc, with fixed diameter/width of 10 µm; and varied centre-to-centre spacing (d) and number of electrodes (N) in the array. The on-chip microelectrochemical cell structure has been designed to facilitate further WE biomodifications. Firstly, the developed microelectrochemical cell does not require packaging hence reducing the production cost and time. Secondly, the working electrode (WE) on the microelectrochemical cell is positioned towards the end of the chip enabling modification of the working electrode surface to be carried out for surface bio-functionalisation without affecting both the RE and CE surface conditions. The developed on-chip microelectrochemical cell was examined with scanning electron microscopy (SEM) and characterised by two electrochemical techniques. Both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed in 1 mM ferrocenecarboxylic acid (FCA) in 0.01 M phosphate buffered saline (PBS) solution at pH7.4. Electrochemical experiments showed that in the case of halving the interspacing distance of the microdisc WE array (50 nm instead of 100 nm), the voltammogram shifted from a steady-state CV (feature of hemispherical diffusion) to an inclined peak-shaped CV (feature of linear diffusion) albeit the arrays had the same surface area. In terms of EIS it was also found that linear diffusion dominates the surface instead of hemispherical diffusion once the interspacing distance was reduced, supporting the fact that closely packed arrays may behave like a macroelectrode

Detection of malachite green and leuco-malachite green in fishery industry

This article summarises the current methods for total malachite green (MG) detectionwhich is known as a sum of MG and leuco-malachite green (LMG) that has been used extensively in aquaculture as fungicide, dye color in textile and other purposes in food industries. LMG is a reducing form of MG, where the MG is easily reduced due to the photo-oxidative de-methylation process. Nevertheless, the use of MG had become an issue due to its toxicity effects. Many analytical instruments such as HPLC, LC-MS/MS, GC-MS, and spectrometry have been widely used for detection of MG. However, these methods require long time sample preparation and analysis, expensive, use hazardous reagents and indirect measurements. Hence, other analytical methods which are more sensitive, safe, rapid, inexpensive andportable are required. Alternatively, biosensors promise a more sensitive and rapid detection method for MG and LMG

Chemically modified electrodes for recessed microelectrode array

Chemical modifications on recessed microelectrode array, achieved via electrodeposition techniques are reported here. Silicon-based gold microelectrode arrays of 10µm microband and microdisc array were selected and functionalised using sol-gel and nanoporous gold (NPG) respectively. For electrochemically assisted self-assembly (EASA) formati6154on of sol-gel, electrode surface was first pre-treated with a self-assembled partial monolayer of mercaptopropyltrimethoxysilane (MPTMS) before transferring it into the sol containing cetyltrimethyl ammonium bromide (CTAB)/tetraethoxysilane (TEOS):MPTMS (90:10) precursors. A cathodic potential is then applied. It was found that larger current densities were required in ensuring successful film deposition when moving from macro- to micro- dimensions. For NPG modification, a chemical etching process called dealloying was employed. NPG of three different thicknesses have been successfully deposited. All the modified and functionalized microelectrode arrays were characterized by both optical (SEM) and electrochemical analysis (cyclic voltammetry and impedance spectroscopy). An increase in surface area and roughness has been observed and such will benefit for future sensing application

Immunosensing of Aflatoxin B1 and Ochratoxin A on a Portable Device as Point-of-Care

Aflatoxin B1 (AFB1) and ochratoxin A (OTA) are potent mycotoxins produced by the fungal genus Aspergillus. Their occurrence in grain corn is alarming hence the need for rapid on-site detection. An immuno-based biosensor technique for detection of the aforementioned toxins is described here. Highly specific in-house polyclonal antibodies against AFB1 and OTA were employed as bioreceptors in a label-free electrochemical biosensor; immobilized on modified screen-printed carbon electrodes (SPCEs). The immuno-functionalized SPCEs were first characterized on a laboratory electrochemical workstation for proof-on-concept study using differential pulse voltammetry (DPV) electrochemical technique. An Android-based device is improvised as a portable electrochemical reader integrated with internet of thing (IoT) features which include cloud server and a dedicated website. Sensitivity achieved by the modified SPCEs on the portable device is superior compared to enzyme-linked immunosorbent assay (ELISA) method and lab-based electrochemical workstation. The miniaturized biosensor system has been successfully tested on cornfield for in-situ mycotoxins detection with simple sample extraction. Analysis performed on twenty samples were validated using chromatographic analysis. This biosensor-IoT system offers a potential application for real-time detection and the portable reader serves as an excellent tool for point-of-care in routine monitoring of harmful mycotoxins

Serial evaluation of sequential organ failure assessment score in predicting 1-year mortality in critically Ill patients

Introduction: The prediction of long-term prognosis or outcome of critically ill patients in the intensive care unit (ICU) is important for prognostication and administration purposes. The Sequential Organ Failure Assessment (SOFA) score was developed in order to estimate organ failure in patients with sepsis. Organ failures have been associated with mortality and hence SOFA score has been validated as an outcome measure. To the best of our knowledge, the association of SOFA, and serial SOFA score with 1-year mortality has not been well established. Materials and method: This was a retrospective observational cross sectional study using the existing record of patients admitted to the general ICU at the Sultan Ahmad Shah Medical Centre from the 1st June 2017 to the 30th May 2018. Data was collected from daily clinical charts and medical records of patients. SOFA score on day-1, day-3, day-3, and on discharge were recorded and subsequently delta SOFA was calculated. Results: Data from a total of 120 patients were collected. SOFA score within 3 days of admission predicted 1-year mortality, with the highest prediction for on SOFA score on discharge from ICU. Serial SOFA score measured within 24 hours (day-1 to day-2) and 48 hours (day-1 to day-3) did not predict mortality; however, delta SOFA involving SOFA on discharge did. Cardiovascular and renal scores were the most significant individual component of SOFA score that contributed to 1-year mortality. Conclusion: SOFA score measured on discharge from ICU plays a key important factor in contributing for the prediction of 1-year mortality. Cardiovascular and renal scores were the most significant component that warrant risk stratification measures using the parameters