Palanisamy Kannan

Highly stable and sensitive glucose biosensor based on covalently assembled high density Au nanostructures

We describe the development of a highly stable and sensitive glucose biosensor based on the nanohybrid materials derived from gold nanoparticles (AuNPs) and multi-walled carbon nanotubes (MWCNT). The biosensing platform was developed by using layer-by-layer (LBL) self-assembly of the nanohybrid materials and the enzyme glucose oxidase (GOx). A high density of AuNPs and MWCNT nanocomposite materials were constructed by alternate self assembly of thiol functionalized MWCNTs and AuNPs, followed by chemisoption of GOx. The surface morphology of multilayered AuNPs/MWCNT structure was characterized by field emission-scanning electron microscope (FE-SEM), and the surface coverage of AuNPs was investigated by cyclic voltammetry (CV), showing that 5 layers of assembly achieves the maximum particle density on electrode. The immobilization of GOx was monitored by electrochemical impedance spectroscopy (EIS). CV and amperometry methods were used to study the electrochemical oxidation of glucose at physiological pH 7.4. The Au electrode modified with five layers of AuNPs/MWCNT composites and GOx exhibited an excellent electrocatalytic activity towards oxidation of glucose, which presents a wide liner range from 20 μM to 10 mM, with a sensitivity of 19.27 μA mM(-1) cm(-2). The detection limit of present modified electrode was found to be 2.3 μM (S/N=3). In addition, the resulting biosensor showed a faster amperometric current response (within 3 s) and low apparent Michaelis-Menten constant (K(m)(app)). Our present study shows that the high density of AuNPs decorated MWCNT is a promising nanohybrid material for the construction of enzyme based electrochemical biosensors.

Gold Nanorods as Colorful Chromogenic Substrates for Semiquantitative Detection of Nucleic Acids, Proteins, and Small Molecules with the Naked Eye

Herein, we report for the first time a colorful chromogenic substrate, which displays vivid color responses in the presence of different concentration of analytes. Our investigation reveals that the selective shortening of gold nanorods (AuNRs) could generate a series of distinct colors that covers nearly the whole visible range from 400 to 760 nm. These vivid colors can be easily distinguished by the naked eye; as a result, the accuracy of visual inspection could be greatly improved. Next, we demonstrate the utility of AuNRs as multicolor chromogenic substrate to develop a number of colorimetric immunoassay methods, e.g., multicolor enzyme-linked immunosorbent assay (ELISA), multicolor competitive ELISA, and multicolor magnetic immunoassay (MIA). These methods allow us to visually quantify the concentration of a broad range of target molecules with the naked eye, and the obtained results are highly consistent with those state-of-the-art techniques that are tested by the sophisticated apparatus. These multicolor portable and cost-effective immunoassay approaches could be potentially useful for a number of applications, for example, in-home personal healthcare, on-site environmental monitoring, and food inspection in the field.

Enhanced emission of NaYF4:Yb,Er/Tm nanoparticles by selective growth of Au and Ag nanoshells

We report a novel, simple strategy to efficiently enhance the fluorescence of metal-coated up-conversion nanoparticles (UCNPs), NaYF4:Yb,Er/Tm. The UCNPs are functionalized with a polyamidoamine generation 1 (PAMAM G1) dendrimer, followed by a continuous growth of gold (Au) or silver (Ag) nanoshells to selectively enhance the up-converted green, violet and blue emissions (>20 fold).

Ultrasensitive detection of L-cysteine using gold-5-amino-2-mercapto-1,3,4-thiadiazole core-shell nanoparticles film modified electrode.

We are reporting the selective, sensitive and stable determination of L-cysteine (CY) at physiological pH (pH=7.2) using a gold-aminomercaptothiadiazole core-shell nanoparticles (p-GAMCS NPs) film modified GC electrode. The p-GAMCS NPs film was fabricated on GC electrode by potentiodynamic method using 5-amino-2-mercapto-1,3,4-thiadiazole stabilized gold nanoparticles (AMT-AuNPs). The fabricated p-GAMCS NPs film was characterized by cyclic voltammetry and atomic force microscopy (AFM) techniques. The AFM image of the p-GAMCS NPs film showed that it contains a homogeneously distributed AuNPs with a spherical shape of ~10 nm. The p-GAMCS NPs film modified GC electrode was exploited for the determination of CY. The bare GC electrode failed to show any response for CY (pH=7.2) whereas p-GAMCS NPs film on GC electrode showed a well-defined oxidation peak for CY at 0.51 V. Further, p-GAMCS NPs film modified electrode successfully resolved the voltammetric signals of ascorbic acid (AA) and CY with a peak separation of 500 mV. This is the first report for the large voltammetric peak separation between CY and AA to the best of our knowledge. The amperometric current was increased linearly from 10 nM to 140 nM CY with a detection limit of 3 pM (S/N=3). The present modified electrode showed better recoveries for spiked CY into the human blood serum and urine samples.

Highly sensitive amperometric detection of bilirubin using enzyme and gold nanoparticles on sol-gel film modified electrode.

We describe the development of a simple and highly sensitive electrochemical (amperometric) sensing of bilirubin based on bilirubin oxidase (BOx) incorporated into the gold nanoparticles (AuNPs). This nanoelectrode platform with self-assembled enzyme is highly sensitive toward the electrochemical oxidation of bilirubin and increased the bilirubin concentration linearly from 1 to 5000 μM with a correlation coefficient of 0.9960, and an apparent Michaelis constant (K(M,app)) of 44 ± 0.4 μM. Using an amperometric method, the detection limit for bilirubin at the enzyme-modified electrode was 1.4 nM (signal-to-noise ratio=3). The modified electrode retained a stable response for 2 days while losing only ca. 3.4% of its initial sensitivity during a 10 days storage period in 0.2M phosphate buffer solution (pH=8.4) at ≤ 4°C. The practical application of the modified electrode was demonstrated by measuring the concentration of bilirubin in blood serum sample.

Concave gold nanoparticle-based highly sensitive electrochemical IgG immunobiosensor for the detection of antibody–antigen interactions

In this work, we report a novel electrochemical sensor for the label-free, real time and highly sensitive detection of antibody–antigen interactions based on concave gold nanocuboids (CAuNCs). In contrast to low-index facet gold nanoparticles (AuNPs) such as gold nanorods (AuNRs), the CAuNCs provide higher surface atoms with enhanced chemical activities, which can efficiently catalyse the oxidation reaction of amino groups on antibodies (anti-bovine IgG produced in rabbit). This leads to an obvious redox current response being observed in cyclic voltammetry (CV) measurements. Upon the introduction of an IgG antigen, a notable decrease of the anodic peak current was observed, which is attributed to the formation of an antigen–antibody complex between the IgG antigen and the antibody on the CAuNCs. The unique electrocatalytic property of the CAuNCs allows easy detection of the rabbit IgG antigen in a wide range of concentrations (from 10 to 200 ng mL−1), with a limit of detection (LOD) to 5 ng mL−1 (signal to noise ratio 3 (S/N = 3)) by using a CV method.

Highly sensitive electrochemical determination of neutrophil gelatinase-associated lipocalin for acute kidney injury

A label-free electrochemical immunosensor for the detection of neutrophil gelatinase-associated lipocalin (NGAL) is developed by the immobilization of rabbit polygonal lipocalin-2 antibody on gold nanoparticles attached on generation-1polyamidoamine (PAMAM) dendrimer (LA2/AuNPs/PAMAM)-modified gold electrode. The modification procedure was characterized by UV-vis, surface enhanced Raman spectroscopy and field-emission scanning electron microscopy techniques. The detection of NGAL is based on the enhancement of oxidation current on the modified electrodes upon the antigen-antibody interaction. The electrochemical immunosensor exhibited high sensitivity (1 ng mL(-1) (280 pM) based on the signal-to-noise ratio 3), wide linear range (50-250 ng mL(-1)) and long-term stability. The reliability of the developed immunosensor was investigated by the detection of NGAL in both blood serum and urine samples.

Direct growth of highly branched crystalline Au nanostructures on an electrode surface: their surface enhanced Raman scattering and electrocatalytic applications

This paper reports a simple, one-step, template-free surface assisted growth of crystalline branched-like Au nanoparticles (three-dimensional (3-D) growth with more than 12 tips) with high yield and good size monodispersity at room temperature. The size of the Au branched nanocrystals could be tuned by controlling the composition of the starting reaction mixture (growth solution). The key surface growth strategy was to use a 1,6-hexanedithiol (HDT) monolayer-modified electrode immersed into growth solution to confine the growth of the branched Au nanocrystals on their surface. Time-course measurements by field emission-scanning electron microscopy (FESEM) were used to follow the reaction progress and the evolution of the branched-like nanocrystal shape. The Au nanocrystals exhibited strong surface enhanced effects which were utilized in the design of an efficient, stable, and Raman-active tag for biosensors, and electrocatalytic applications.

Tungsten carbide nanotubes supported platinum nanoparticles as a potential sensing platform for oxalic acid.

Supported tungsten carbide is an efficient and vital nanomaterial for the development of high-performance, sensitive, and selective electrochemical sensors. In this work, tungsten carbide with tube-like nanostructures (WC NTs) supported platinum nanoparticles (PtNPs) are synthesized and explored as an efficient catalyst toward electrochemical oxidation of oxalic acid for the first the time. The WC NTs supported PtNPs modified glassy carbon (GC) electrode is highly sensitive toward the electrochemical oxidation of oxalic acid. A large decrease in the oxidation overpotential (220 mV) and significant enhancement in the peak current compared to unmodified and Pt/C modified GC electrodes have been observed without using any redox mediator. Moreover, WC NTs supported PtNPs modified electrode possessed wide linear concentration ranges from 0 to 125 nM and a higher sensitivity toward the oxidation of oxalic acid (80 nA/nM) achieved by the amperometry method. The present modified electrode showed an experimentally determined lowest detection limit (LOD) of 12 nM (S/N = 3). Further, WC NTs supported PtNPs electrode can be demonstrated to have an excellent selectivity toward the detection of oxalic acid in the presence of a 200-fold excess of major important interferents. The practical application of WC NTs supported PtNPs has also been demonstrated in the detection of oxalic acid in tomato fruit sample, by differential pulse voltammetry under optimized conditions.

Close-packed assemblies of discrete tiny silver nanoparticles on triangular gold nanoplates as a high performance SERS probe

Bimetallic nanocatalysts often display enhanced physical and chemical properties compared to those of their monometallic counterparts. Herein, we introduce a simple method to fabricate an island like array of tiny Ag nanoparticles bounded on triangular Au nanoplates as the surface-enhanced Raman scattering (SERS) substrate. The surface morphology of the synthesized nanoparticles was characterized via field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). Rhodamine 6G (R6G) is used as a model analyte to evaluate the performance of the tiny Ag nanoparticle bounded triangular Au nanoplates as a SERS-active substrate and validate the SERS effect. The fabricated SERS substrate showed drastically enhanced intensity with a SERS enhancement factor as high as 107, which is enough to detect a single molecule, and excellent reproducibility (less than ±5%) of the signal intensity. This is because of the island-like tiny Ag nanoparticle bounded triangular Au nanoplates and their large number of “hot spots”. This substrate could also be used for label-free immunoassays, biosensing, and nanoscale optical antennas and light sources.