Bioanalysis based on glutamate dehydrogenase/diaphorase system for ammonium determination (Bioanalisis berasaskan sistem glutamat dehidrogenase-diaporase untuk pengesanan ammonium)

Bioanalisis bagi pengesanan ammonium berdasarkan penggunaan sistem dua enzim Glutamat dehidrogenase-Diaporase (GLDH-Dph) dan reagen tiazolil biru tetrazolium bromida (MTT) diterangkan. Dalam kajian ini, GLDH memangkinkan tindak balas penukaran asid α-ketoglutarik membentuk L-glutamat dan kofaktor β-nikotinamida adenina dinukleotida (NADH) akan dioksidakan kepada NAD+ dengan kehadiran ammonium. Seterusnya, baki NADH yang tidak digunakan dioksidakan kepada NAD+ oleh Dph dan MTT dan diturunkan kepada formazan yang berwarna ungu. Keamatan formazan yang terbentuk dicerap menggunakan spektrofotometer pada panjang gelombang 563 nm. Bioanalisis ini memberikan rangsangan yang optimum bagi pengesanan ammonium pada pH larutan penimbal fosfat bersamaan 8, kepekatan GLDH, Dph dan reagen MTT pada 13.2 unit/mL, 1.17 unit/mL dan 0.2 mM, masing-masing. Bioanalisis ini memberikan rangsangan linear terhadap ammonium dalam julat kepekatan 3 - 50 μM dengan had pengesanan 1 μM

An approach of zirconium oxide/polyethylene glycol nanocomposite film on screen printed carbon electrode and its application in glucose determination

An amperometric biosensor for the quantitative measurement of glucose is reported. The biosensor is based on a biocomposite that is homogeneous and easily prepared. This biocomposite is made of polyethylene glycol (PEG), Cetyl trimethylammonium bromide (CTAB), glucose oxidase (GOx), and zirconium oxide (ZrO2) nanoparticles. Effect of applied potential, pH, nanocomposite layer, ratio of zirconium oxide nanoparticles (ZrO2) to polyethylene glycol (PEG), concentration of ferrocenecarboxaldehyde (Fc) and concentration of enzyme that governed the analytical performance of the biosensor have been studied. The biosensor was applied to detect glucose with a linear calibration range from 0.1 mM to 12 mM and limit of detection 0.04 mM. The variation coefficient (RSD) for repeatability was 7.5% for ten successive assays while 6.01% (n = 5) for reproducibility test demonstrating that the biosensor fabrication process is reproducible. Common interfering compounds on the amperometric response of the sensor were investigated and discussed herein

A simple and sensitive fluorescence based biosensor for the determination of uric acid using H2O2-sensitive quantum dots/dual enzymes

A novel optical detection system consisting of combination of uricase/HRP–CdS quantum dots (QDs) for the determination of uric acid in urine sample is described. The QDs was used as an indicator to reveal fluorescence property of the system resulting from enzymatic reaction of uricase and HRP (horseradish peroxidase), which is involved in oxidizing uric acid to allaintoin and hydrogen peroxide. The hydrogen peroxide produced was able to quench the QDs fluorescence, which was proportional to uric acid concentration. The system demonstrated sufficient activity of uricase and HRP at a ratio of 5U:5U and pH 7.0. The linearity of the system toward uric acid was in the concentration range of 125–1000 µM with detection limit of 125 µM

Synthesis and surface modification of biocompatible water soluble core-shell quantum dots

In this study, the applications of CdSe/ZnS quantum dots (QDs) and its role in advanced sensings has been explored. The CdSe/ZnS was synthesized by using hot injection method with the shell ZnS layer was made using successive ionic layer adsorption and reaction (SILAR) method. The morphology of the CdSe/ZnS QDs was studied using Transmission Electron Microscope (TEM) and the average particle size was in 10-12 nm range. The prepared QDs were optically characterized using spectrofluorescence and strong emission was observed at 620 nm. Comparison of the fluorescence emissions of CdSe/ZnS capped with various capping ligands such as L-cysteine, thioglycolic acid (TGA), mercaptopropionic acid (MPA), mercaptosuccinic acid (MSA) and mercaptoundecanoic acid (MUA) were studied. The CdSe/ZnS capped with TGA gave the strongest fluorescence emission compared to others

Thiolate-Capped CdSe/ZnS Core-Shell Quantum Dots for the Sensitive Detection of Glucose

A semiconducting water-soluble core-shell quantum dots (QDs) system capped with thiolated ligand was used in this study for the sensitive detection of glucose in aqueous samples. The QDs selected are of CdSe-coated ZnS and were prepared in house based on a hot injection technique. The formation of ZnS shell at the outer surface of CdSe core was made via a specific process namely, SILAR (successive ionic layer adsorption and reaction). The distribution, morphology, and optical characteristics of the prepared core-shell QDs were assessed by transmission electron microscopy (TEM) and spectrofluorescence, respectively. From the analysis, the results show that the mean particle size of prepared QDs is in the range of 10–12 nm and that the optimum emission condition was displayed at 620 nm. Further, the prepared CdSe/ZnS core shell QDs were modified by means of a room temperature ligand-exchange method that involves six organic ligands, L-cysteine, L-histidine, thio-glycolic acid (TGA or mercapto-acetic acid, MAA), mercapto-propionic acid (MPA), mercapto-succinic acid (MSA), and mercapto-undecanoic acid (MUA). This process was chosen in order to maintain a very dense water solubilizing environment around the QDs surface. From the analysis, the results show that the CdSe/ZnS capped with TGA (CdSe/ZnS-TGA) exhibited the strongest fluorescence emission as compared to others; hence, it was tested further for the glucose detection after their treatment with glucose oxidase (GOx) and horseradish peroxidase (HRP) enzymes. Here in this study, the glucose detection is based on the fluorescence quenching effect of the QDs, which is correlated to the oxidative reactions occurred between the conjugated enzymes and glucose. From the analysis of results, it can be inferred that the resultant GOx:HRP/CdSe/ZnS-TGA QDs system can be a suitable platform for the fluorescence-based determination of glucose in the real samples

Preparation of modified CdSe/ZnS quantum dots and gold nanoparticles for glucose and dengue detection

Development of sensors combined with nanomaterials becoming an interesting area due to their unique optical properties. In this research, two different biosensor utilizing CdSe/ZnS quantum dots (QDs) and gold nanoparticles (AuNPs) have been developed and successfully applied to detect glucose and dengue virus DNA, respectively. CdSe/ZnS QDs is utilized in our first prepared biosensor for glucose monitoring. The CdSe/ZnS QDs was successfully prepared via hot injection method while the ZnS layer was made using the successive ionic layer adsorption and reaction (SILAR) method. The prepared QDs was spherical monodisperse with uniform sizes of 3 to 3.2 nm and 10 to 12 nm for CdSe core QDs and CdSe/ZnS core-shells QDs, respectively. The prepared CdSe/ZnS QDs has been modified with organic ligand for glucose analysis. Detection was performed using glucose concentrations ranging from 0 to 40 mM with linear relationship was observed from 0 to 10 mM (with R2 = 0.9964) and limit of detection was obtained at 0.3 mM. Comparison between our developed biosensor with commercialized assay kit result in 99% similarity thus indicated that the developed biosensor utilizing CdSe/ZnS QDs was reliable for the detection of glucose. AuNPs is utilized in our second prepared biosensor for dengue virus detection. Positively charged AuNPs was interacting with negatively charged PNA/DNA hybridised biochip via electrostatic interaction and successfully used to detect dengue virus using both naked eye and optical scanner. Detection of dengue virus was study using concentration ranging from 10 pM to 1 μM with a detection limit was obtained at 10 pM. Repeatability and reproducibility study gave relative standard deviations (RSD) less than 5% in all measurements, which indicate that the chips produced in this study are suitable for mass fabrication of devices with similar responses. Comparison study between our developed PNA/DNA biochip with real time RT-PCR was investigated and obtaining 88% agreement. Both scopes covered in this study give new possibilities for healthcare monitoring, where these studies improved the specificity and selectivity of the developed biosensor

Thiolate-capped CdSe/ZnS core-shell quantum dots for the sensitive detection of glucose

A semiconducting water-soluble core-shell quantum dots (QDs) system capped with thiolated ligand was used in this study for the sensitive detection of glucose in aqueous samples. The QDs selected are of CdSe-coated ZnS and were prepared in house based on a hot injection technique. The formation of ZnS shell at the outer surface of CdSe core was made via a specific process namely, SILAR (successive ionic layer adsorption and reaction). The distribution, morphology, and optical characteristics of the prepared core-shell QDs were assessed by transmission electron microscopy (TEM) and spectrofluorescence, respectively. From the analysis, the results show that the mean particle size of prepared QDs is in the range of 10–12 nm and that the optimum emission condition was displayed at 620 nm. Further, the prepared CdSe/ZnS core shell QDs were modified by means of a room temperature ligand-exchange method that involves six organic ligands, L-cysteine, L-histidine, thio-glycolic acid (TGA or mercapto-acetic acid, MAA), mercapto-propionic acid (MPA), mercapto-succinic acid (MSA), and mercapto-undecanoic acid (MUA). This process was chosen in order to maintain a very dense water solubilizing environment around the QDs surface. From the analysis, the results show that the CdSe/ZnS capped with TGA (CdSe/ZnS-TGA) exhibited the strongest fluorescence emission as compared to others; hence, it was tested further for the glucose detection after their treatment with glucose oxidase (GOx) and horseradish peroxidase (HRP) enzymes. Here in this study, the glucose detection is based on the fluorescence quenching effect of the QDs, which is correlated to the oxidative reactions occurred between the conjugated enzymes and glucose. From the analysis of results, it can be inferred that the resultant GOx:HRP/CdSe/ZnS-TGA QDs system can be a suitable platform for the fluorescence-based determination of glucose in the real samples

Amperometric biosensor based on zirconium oxide/polyethylene glycol/tyrosinase composite film for the detection of phenolic compounds

A phenolic biosensor based on a zirconium oxide/polyethylene glycol/tyrosinase composite film for the detection of phenolic compounds has been explored. The formation of the composite film was expected via electrostatic interaction between hexacetyltrimethylammonium bromide (CTAB), polyethylene glycol (PEG), and zirconium oxide nanoparticles casted on screen printed carbon electrode (SPCE). Herein, the electrode was treated by casting hexacetyltrimethylammonium bromide on SPCE to promote a positively charged surface. Later, zirconium oxide was mixed with polyethylene glycol and the mixture was dropped cast onto the positively charged SPCE/CTAB. Tyrosinase was further immobilized onto the modified SPCE. Characterization of the prepared nanocomposite film and the modified SPCE surface was investigated by scanning electron microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and Cyclic voltamogram (CV). The developed biosensor exhibits rapid response for less than 10 s. Two linear calibration curves towards phenol in the concentrations ranges of 0.075-10 µM and 10-55 µM with the detection limit of 0.034 µM were obtained. The biosensor shows high sensitivity and good storage stability for at least 30 days