Ravi Kumar Arun

A paper based microfluidic device for the detection of arsenic using a gold nanosensor

A paper based microfluidic device is fabricated that can rapidly detect very low concentrations of As3+ ions using a gold nanosensor, Au–TA–TG. This simple but efficient system develops a visible bluish-black colour precipitate due to the formation of nanoparticle aggregates through transverse diffusive mixing of Au–TA–TG with As3+ ions on a paper substrate. The approach is extremely selective for arsenic with a detection limit of 1.0 ppb, which is lower than the WHOs reference standard for drinking water.

Smart gold nanosensor for easy sensing of lead and copper ions in solution and using paper strips

A smart gold nanosensor, Au–TA–DNS is designed that can rapidly detect very low concentrations of Pb2+ and Cu2+ ions. The nanosensor develops a visible blue colour in solution and on paper strips, because of the formation of nanoparticle aggregates upon binding with metal ions. Due to the presence of dansyl fluorophore, Au–TA–DNS also exhibits significant fluorescence quenching following Pb2+ and Cu2+ binding in aqueous medium, which is proportional to the concentration of ions. Both colorimetric and fluorometric analyses are very much selective for lead and copper ions with a detection limit of ≤10.0 ppb. The paper based sensing method has the advantage of cost-effectiveness and would be useful for wide range of field-test applications such as water quality monitoring process.

Silver Nanoparticles in Comparison with Ionic Liquid and rGO as Gate Dopant for Paper–Pencil-Based Flexible Field-Effect Transistors

Nanoparticle-based flexible field-effect transistors (FETs) containing carbon nanotubes (CNTs) and silicon nanowires (SiNWs) have attracted tremendous attention, since their interesting device performance can be utilized for integrated nanoscale electronics. However, use of CNTs and SiNWs on polymer substrates poses serious limitations in terms of their fabrication procedure, repeatability, and biodegradability. In this article, we report for the first time the fabrication and characteristics of solution-processed FETs on a paper substrate doped with easily prepared silver nanoparticles (AgNPs). To compare the FET performance, we fabricated two other FETs on paper containing ionic liquid (IL, 1-butyl-3-methylimidazolium octyl sulfate) and reduced graphene oxide (rGO) as dopants. We observe that the AgNP-based dopant generated good FET characteristics in terms of linear transconductance variations and higher carrier concentration values, showing negligible changes after bending and aging. In comparison with the AgNP-FET, the rGO- and IL-based dopants yielded high carrier mobilities, but the rGO-based FET is more susceptible to aging and bending. The excellent linearity of the IDS–VG curve found for the AgNP-FET ensures its applicability for devices requiring linear transfer characteristics such as linear amplifiers.

Novel synthesis of a mixed Cu/CuO–reduced graphene oxide nanocomposite with enhanced peroxidase-like catalytic activity for easy detection of glutathione in solution and using a paper strip

A reduced graphene oxide (rGO) based mixed copper nanocomposite, Cu/CuO–rGO is prepared through a novel synthetic approach: a simple one-step oxidation–reduction reaction between aqueous graphene oxide (GO) and copper(II) chloride (CuCl2) solutions at ambient temperature and pressure. The nanocomposite shows enhanced peroxidase-like catalytic activity by rapidly catalyzing a TMB (3,3′,5,5′-tetramethyl benzidine)–H2O2 reaction that develops a visible blue color in solution due to the oxidation of TMB. The catalyst follows a Michaelis–Menten reaction mechanism and exhibits strong affinity towards both H2O2 and TMB. The blue color developed by the Cu/CuO–rGO–TMB–H2O2 system becomes colorless in solution when glutathione is present even at a very low concentration (0.032 μM). This distinct color change provides the basis of the present colorimetric method for highly sensitive and selective detection of GSH in solution as well as on a paper-strip within a <5 min time period. The use of Cu/CuO–rGO as an enzyme-like catalyst in TMB–H2O2 mediated GSH sensing process shows the benefits of simplicity, cost-effectiveness and provides an alternative non-enzymatic way of glutathione estimation in real samples such as commercially available tablets and human blood plasma.

Paper-PDMS hybrid microchannel: a platform for rapid fluid-transport and mixing

The functionalities of a paper-PDMS hybrid microchannel, as a potential fluidic transport platform, are presented. The setup consists of a PDMS microchannel with one of its walls covered by paper. In contrast to the available microfluidic platforms, the capillary filling is found to occur at much faster speed in the hybrid channel. Moreover, experimentation using two dye solutions shows mixing enhancement at a significantly faster rate and at a shorter distance in the hybrid channel as compared to the other available counterparts. The paper attachment is found to induce an effective slip during liquid transport, and thereby allows faster transport and capillary filling. The liquid slippage further modifies the shear flow behavior near the wall leading to a slip-enhanced mixing within the hybrid channel. These fundamental understandings correspond to the experimental results quantitatively in terms of corroborating scaling laws. Further mixing enhancement is introduced through spiral, curved and elliptical–spiral geometries of the channel. Apart from the above benefits, the enclosed arrangement protects sensitive reagents from external environment and offers better control over their transport, thus giving a stable mixing and reaction performance inside the channel.

Gold Nanostructure in Sensor Technology: Detection and Estimation of Chemical Pollutants

Nanosensors have been proven to be a powerful tool in sensing various targeting analytes such as proteins, DNA, and RNA and small molecules such as toxins, drugs, metabolites, biomarkers, and environmental pollutants with high specificity and selectivity. Among various environmental pollutants, pollution by contamination of heavy metal is one of the most serious issues in current global scenario because of its potential toxicity toward human and aquatic life. Conventional methods of detecting such toxic ions include inductively coupled plasma mass spectroscopy (ICP-MS) and atomic absorption spectroscopy (AAS). These methods are accurate in minute-level detection, but still possess some drawbacks such as high time consumption, involvement of toxic chemicals, and requirement of sophisticated laboratory setup. Therefore, there is a need for inexpensive, user-friendly, quick, and portable methods for detection of these toxic ions. Efforts are being made in developing gold nanosensors for easy monitoring of heavy metal toxins in environmental samples. Due to unique optical, electrical, and mechanical properties, gold nanoparticles render improved performance as sensor probe for better sensitivity, selectivity, portability, and multi-load detection capability. During sensing process, the nanoparticles aggregate in the presence of specific metal ions and show visible color change from red to blue to colorless. The qualitative color change detected using naked eyes shows the presence of targeted heavy metal ions. Apart from the qualitative analysis, the quantitative estimation can be achieved with the help of gold nanoparticles by various techniques such as CCD or CMOS sensors, photodetectors, and color light sensors. This chapter deals with various synthesis processes, potential colorimetric-based sensing applications of gold-based nanosensor, and associated electronic circuitry, which could be employed for detection and quantification of various heavy metal toxins.