Jaafar Abdullah

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.

Chitosan-based tyrosinase optical phenol biosensor employing hybrid nafion/sol-gel silicate for MBTH immobilization.

The development of an optical biosensor based on immobilization of 3-methyl-2-benzothiazolinone hydrazone (MBTH) in hybrid nafion/sol-gel silicate film and tyrosinase in chitosan film for the detection of phenolic compounds has been described. Tyrosinase was immobilized in chitosan film deposited on the hybrid nafion/sol-gel silicate film containing MBTH. The enzymatic oxidation product of phenolic compounds were stabilized through formation of adduct with MBTH to produce a maroon color adduct. The color intensity of adduct was found to increase proportionally with the increase of the substrate concentrations after 5min exposure. The linearity of the biosensor towards phenol, catechol and m-cresol were in the respective concentration range of 0.5-7.0, 0.5-10.0 and 1.0-13.0mg/L with detection limit of 0.18, 0.23 and 0.43mg/L, respectively. The biosensor shows a good stability for at least 3 months.

The development of silicon nanowire as sensing material and its applications

The application of silicon nanowire (SiNW) as a sensing nanomaterial for detection of biological and chemical species has gained attention due to its unique properties. In this review, a short description is also demonstrated on the synthesis techniques of SiNWs and recent progress on sensor development based on electrochemical methods, fluorescence field-effect transistors (FET), and surface-enhanced Raman scattering (SERS) spectroscopy. We also discussed the challenges of SiNW-based sensors in the future.

The utilization of SiNWs/AuNPs-modified indium tin oxide (ITO) in fabrication of electrochemical DNA sensor

This work describes the incorporation of SiNWs/AuNPs composite as a sensing material for DNA detection on indium tin-oxide (ITO) coated glass slide. The morphology of SiNWs/AuNPs composite as the modifier layer on ITO was studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The morphological studies clearly showed that SiNWs were successfully decorated with 20 nm-AuNPs using self-assembly monolayer (SAM) technique. The effective surface area for SiNWs/AuNPs-modified ITO enhanced about 10 times compared with bare ITO electrode. SiNWs/AuNPs nanocomposite was further explored as a matrix for DNA probe immobilization in detection of dengue virus as a bio-sensing model to evaluate its performance in electrochemical sensors. The hybridization of complementary DNA was monitored by differential pulse voltammetry (DPV) using methylene blue (MB) as the redox indicator. The fabricated biosensor was able to discriminate significantly complementary, non-complementary and single-base mismatch oligonucleotides. The electrochemical biosensor was sensitive to target DNA related to dengue virus in the range of 9.0-178.0 ng/ml with detection limit of 3.5 ng/ml. In addition, SiNWs/AuNPs-modified ITO, regenerated up to 8 times and its stability was up to 10 weeks at 4°C in silica gel.

In vivo tumor targeting and anti-tumor effects of 5-fluororacil loaded, folic acid targeted quantum dot system

In this study, we modulated the anti-cancer efficacy of 5-Fluorouracil (5-FU) using a carrier system with enhanced targeting efficacy towards folate receptors (FRs) expressing malignant tissues. The 5-FU drug was loaded onto Mn-ZnS quantum dots (QDs) encapsulated with chitosan (CS) biopolymer and conjugated with folic acid (FA) based on a simple wet chemical method. The formation of 5-FU drug loaded composite was confirmed using Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Furthermore, the in vivo biodistribution and tumor targeting specificity of the 5-FU@FACS-Mn:ZnS in the tumor-bearing mice was conducted based on the Zn(2+) tissue bioaccumulation using inductively coupled plasma (ICP) spectroscopy. In addition to the characterization, the in vitro release profile of 5-FU from the conjugates investigated under diffusion controlled method demonstrated a controlled release behaviour as compared against the release behaviour of free 5-FU drug. The as-synthesized 5-FU@FACS-Mn:ZnS nanoparticle (NP) systemically induced higher level of apoptosis in breast cancer cells in vitro as compared to cells treated with free 5-FU drug following both cell cycle and annexin assays, respectively. Also, the in vivo toxicity assessment of the 5-FU@FACS-Mn:ZnS NPs as compared to the control did not cause any significant increase in the activities of the liver and kidney function biomarkers, malondialdehyde (MDA) and nitric oxide (NO) levels. However, based on the FA-FRs chemistry, the 5-FU@FACS-Mn:ZnS NPs specifically accumulated in the tumor of the tumor-bearing mice and thus contributed to the smaller tumor size and less event of metastasis was observed in the lungs when compared to the tumor-bearing mice groups treated with the free 5-FU drug. In summary, the results demonstrated that the 5-FU@FACS-Mn:ZnS QDs exhibits selective anti-tumor effect in MDA-MB231 breast cancer cells in vitro and 4TI breast cancer cells in vivo, providing a blueprint for improving the 5-FU efficacy and tumor targeting specificity with limited systemic toxicity.

Construction of an electrochemical sensor based on carbon nanotubes/gold nanoparticles for trace determination of amoxicillin in bovine milk

In this work, a novel electrochemical sensor was fabricated for determination of amoxicillin in bovine milk samples by decoration of carboxylated multi-walled carbon nanotubes (MWCNTs) with gold nanoparticles (AuNPs) using ethylenediamine (en) as a cross linker (AuNPs/en-MWCNTs). The constructed nanocomposite was homogenized in dimethylformamide and drop casted on screen printed electrode. Field emission scanning electron microscopy (FESEM), energy dispersive X-Ray (EDX), X-Ray diffraction (XRD) and cyclic voltammetry were used to characterize the synthesized nanocomposites. The results show that the synthesized nanocomposites induced a remarkable synergetic effect for the oxidation of amoxicillin. Effect of some parameters, including pH, buffer, scan rate, accumulation potential, accumulation time and amount of casted nanocomposites, on the sensitivity of fabricated sensor were optimized. Under the optimum conditions, there was two linear calibration ranges from 0.2–10 µM and 10–30 µM with equations of Ipa (µA) = 2.88C (µM) + 1.2017; r = 0.9939 and Ipa (µA) = 0.88C (µM) + 22.97; r = 0.9973, respectively. The limit of detection (LOD) and limit of quantitation (LOQ) were calculated as 0.015 µM and 0.149 µM, respectively. The fabricated electrochemical sensor was successfully applied for determination of Amoxicillin in bovine milk samples and all results compared with high performance liquid chromatography (HPLC) standard method.

Sensitive detection of multiple pathogens using a single DNA probe

A simple but promising electrochemical DNA nanosensor was designed, constructed and applied to differentiate a few food-borne pathogens. The DNA probe was initially designed to have a complementary region in Vibrio parahaemolyticus (VP) genome and to make different hybridization patterns with other selected pathogens. The sensor was based on a screen printed carbon electrode (SPCE) modified with polylactide-stabilized gold nanoparticles (PLA-AuNPs) and methylene blue (MB) was employed as the redox indicator binding better to single-stranded DNA. The immobilization and hybridization events were assessed using differential pulse voltammetry (DPV). The fabricated biosensor was able to specifically distinguish complementary, non-complementary and mismatched oligonucleotides. DNA was measured in the range of 2.0×10(-9)-2.0×10(-13)M with a detection limit of 5.3×10(-12)M. The relative standard deviation for 6 replications of DPV measurement of 0.2µM complementary DNA was 4.88%. The fabricated DNA biosensor was considered stable and portable as indicated by a recovery of more than 80% after a storage period of 6 months at 4-45°C. Cross-reactivity studies against various food-borne pathogens showed a reliably sensitive detection of VP.

A Novel Disposable Biosensor Based on SiNWs/AuNPs Modified-Screen Printed Electrode for Dengue Virus DNA Oligomer Detection

In this paper, a disposable screen-printed gold electrode (SPGE) utilized of silicon nanowires (SiNWs) and gold nanoparticles as sensing material was fabricated for detection of DNA oligomers related to dengue virus. First, SiNWs/AuNPs-SPGE was developed by the dispersion of SiNWs in 3-aminopropyltriethoxysilane (0.5%) onto bare SPGE. Second, the AuNPs decoration on SiNWs-SPGE surface was functionalized using dithiopropionic acid through a self-assembly monolayer technique. The electrochemical response of methylene blue (MB) as a redox indicator toward synthetic DNA oligomer after hybridization on SiNWs/AuNPs-SPGE was recorded by cyclic voltammetry and differential pulse voltammetry techniques. The results demonstrated that the reduction peak current of MB was significantly decreased after DNA hybridization process. In addition, the developed biosensor showed a good storage stability and could achieve a linear range of 1 × 10-11 - 1 × 10-7 M (R = 0.98) with the detection limit of 1.63 × 10-12 M.

Electrochemical sensor based on gold nanoparticles/ethylenediamine-reduced graphene oxide for trace determination of fenitrothion in water

In this work, a new procedure was investigated for the production of a reduced graphene oxide/gold nanoparticle (rGO/AuNP) nanocomposite for use as an ideally polarizable modifier in electrochemical sensors. Ethylenediamine (en) was used for reducing the active functional groups (epoxy and carboxylic) of graphene oxide (GO) and as a cross linker for the formation of AuNPs during chemical reduction with sodium citrate. The constructed nanocomposite (AuNP/en-rGO) was easily homogenized in dimethylformamide (DMF) and characterized using different techniques. AuNP/en-rGO was drop-cast on a screen-printed electrode (SPE) as an efficient electrochemical sensor for the highly sensitive determination of fenitrothion. The differential pulse voltammetry (DPV) response of the AuNP/en-rGO-modified SPE under optimized conditions was linear in the range of 0.1–6.25 ng mL−1 with a limit of detection of 0.036 ng mL−1 (S/N = 3). The AuNP/en-rGO-modified SPE showed a selective amperometry response toward fenitrothion among other interfering pesticides. In addition, the sensor was successfully employed for determining the fenitrothion residue in some water samples, including tap and lake waters, and the results were in agreement with those using gas chromatography as the standard test method.

Surface modifications to boost sensitivities of electrochemical biosensors using gold nanoparticles/silicon nanowires and response surface methodology approach

This work describes fabrication of a DNA electrochemical sensor utilized of gold nanoparticles/silicon nanowires/indium tin oxide (AuNPs/SiNWs/ITO) as a modified substrate for detection of dengue virus DNA oligomers using methylene blue (MB) as a redox indicator. The response surface methodology (RSM) was applied as one of the advanced optimization methods for fabrication of SiNWs/AuNPs/ITO electrode and immobilization of DNA probes to enhance the sensitivity of DNA detection. Several factors were successfully optimized using RSM, including volume of SiNWs, concentration of dithiopropionic acid (DTPA), volume of AuNPs, DNA probe concentration, and DNA probe immobilization time. RSM approach shows that AuNPs and DNA probe concentration were the prominent factors affecting on the MB current signal and immobilization of DNA probe on AuNPs/SiNWs surface. This new developed sensor was able to discriminate complementary target sequences, noncomplementary and single-base mismatch sequences, for DNA dengue virus detection.