Samsulida Abd Rahman

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.

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.

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.

Cdse/Zns Capped Thiolate for Application in Glucose Sensing

A semiconducting water soluble core-shell quantum dot (QD) capped with thiolated ligand is used in this study for application in glucose sensing. These QDs were prepared in house based on hot injection technique. The ZnS shell at the outer surface of CdSe core QDs is made via specific process namely, SILAR (successive ionic layer adsorption and reaction). The distribution, morphology and optical characteristics of prepared core shell QDs have been assessed by transmission electron microscopy (TEM) and spectrofluorescence, respectively. The results show that the mean particle size of prepared QDs is in the range of 10-12 nm and the optimum emission condition was displayed at 620nm. The prepared CdSe/ZnS core shell QDs were modified by utilizing six organic ligands L-cysteine, L-histidine, thio-glycolic acid (TGA), mercapto-propionic acid (MPA), mercapto-succinic acid (MSA) and mercapto-undecanoic acid (MUA) at room temperature through a ligand-exchange procedure. This ligand exchange process was chosen in order to produce a very dense water solubilizing agent the QDs surrounding surface. The result shows that CdSe/ZnS capped with thioglycolic acid (CdSe/ZnS-TGA) exhibit the strongest fluorescence emission; therefore it was used in advanced sensing application for the detection of glucose. The highly active CdSe/ZnS-TGA was then interacted with Glucose Oxidase enzyme (GOx) and horseradish peroxidase enzyme (HRP). In this study, determination of glucose level is depending on the QDs fluorescence intensity quenching effect, which is correlated to reaction of the conjugated enzyme-QDs. In the presence of 0.1 mM glucose, fluorescence intensity of the bioconjugate QDs was quenched about 12, 000 a.u. This bioconjugated GOX/HRP/QDs-capped TGA was further analyzed with known concentrations of glucose. Quenched fluorescence intensity was proportionate with glucose concentration. The resultant GOX/HRP/QDs-capped TGA system can be a suitable platform for glucose determination in real samples.