Reza Hajian

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.

Fabrication of an Electrochemical Sensor Based on Gold Nanoparticles/Carbon Nanotubes as Nanocomposite Materials: Determination of Myricetin in Some Drinks

In this paper, the electrochemical behavior of myricetin on a gold nanoparticle/ethylenediamine/multi-walled carbon-nanotube modified glassy carbon electrode (AuNPs/en/MWCNTs/GCE) has been investigated. Myricetin effectively accumulated on the AuNPs/en/MWCNTs/GCE and caused a pair of irreversible redox peaks at around 0.408 V and 0.191 V (vs. Ag/AgCl) in 0.1 mol L−1 phosphate buffer solution (pH 3.5) for oxidation and reduction reactions respectively. The heights of the redox peaks were significantly higher on AuNPs/en/MWNTs/GCE compare with MWCNTs/GC and there was no peak on bare GC. The electron-transfer reaction for myricetin on the surface of electrochemical sensor was controlled by adsorption. Some parameters including pH, accumulation potential, accumulation time and scan rate have been optimized. Under the optimum conditions, anodic peak current was proportional to myricetin concentration in the dynamic range of 5.0×10−8 to 4.0×10−5 mol L−1 with the detection limit of 1.2×10−8 mol L−1. The proposed method was successfully used for the determination of myricetin content in tea and fruit juices.

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.

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.

Linear sweep anodic stripping voltammetry: Determination of Chromium (VI) using synthesized gold nanoparticles modified screen-printed electrode

AbstractA highly sensitive electrochemical sensor has been constructed for determination of Cr(VI) with the lowest limit of detection (LOD) reported to date using gold nanoparticles (AuNPs) modified screen-printed electrode (SPE). The modification of SPE by casting pure AuNPs increases the sensitivity for detection of Cr(VI) ion using anodic stripping voltammetry. Cr(VI) ions are reduced to chromium metal on SPE-AuNPs by applying deposition potential of –1.1 V for 180 s. Afterwards, the oxidation peak current of chromium is obtained by linear sweep voltammetry in the range of −1.0 V to 0.2 V. Under the optimized conditions (HClO4, 0.06 mol L−1; deposition potential, –1.1 V; deposition time, 180s; scan rate, 0.1 V s−1), the limit of detection (LOD) was 1.6 pg mL−1. The fabricated electrode was successfully used for detection of Cr(VI) in tap and seawater. Graphical AbstractAn electrochemical sensor has been constructed based on screen-printed electrode (SPE) modified with gold nanoparticles for determination of Cr(VI) ion in water samples. The coupling of anodic striping voltammetry with SPE modified nanostructures enhanced the sensitivity of electrochemical sensor for detection of Cr(VI) ion at low sample volumes.

Label-Free dengue detection utilizing PNA/DNA hybridization based on the aggregation process of unmodified gold nanoparticles

A label-free optical detection method based on PNA/DNA hybridization using unmodified gold nanoparticles (AuNPs) for dengue virus detection has been successfully developed. In this study, no immobilization method is involved and the hybridization of PNA/DNA occurs directly in solution. Unmodified AuNPs undergo immediate aggregation in the presence of neutral charge peptide nucleic acid (PNA) due to the coating of PNA on AuNPs surface. However, in the presence of complementary targets DNA, the hybridization of PNA probe with target DNA forms negatively charged complexes due to the negatively charged phosphate backbone of the target DNA. The negatively charged complexes adsorbed onto the AuNPs surface ensure sufficient charge repulsion, need for AuNPs dispersion, and stability in solution. The detection procedure is a naked eye method based on immediate color changes and also through UV-vis adsorption spectra. The selectivity of the proposed method was studied successfully by single base mismatch and noncomplementary target DNA.

Study on the spectrophotometric detection of free fatty acids in palm oil utilizing enzymatic reactions

In this paper, a comprehensive study has been made on the detection of free fatty acids (FFAs) in palm oil via an optical technique based on enzymatic aminolysis reactions. FFAs in crude palm oil (CPO) were converted into fatty hydroxamic acids (FHAs) in a biphasic lipid/aqueous medium in the presence of immobilized lipase. The colored compound formed after complexation between FHA and vanadium (V) ion solution was proportional to the FFA content in the CPO samples and was analyzed using a spectrophotometric method. In order to develop a rapid detection system, the parameters involved in the aminolysis process were studied. The utilization of immobilized lipase as catalyst during the aminolysis process offers simplicity in the product isolation and the possibility of conducting the process under extreme reaction conditions. A good agreement was found between the developed method using immobilized Thermomyces lanuginose lipase as catalyst for the aminolysis process and the Malaysian Palm Oil Board (MPOB) standard titration method (R2 = 0.9453).