Roli Verma

Detection of heavy metal ions in contaminated water by surface plasmon resonance based optical fibre sensor using conducting polymer and chitosan

Optical fibre surface plasmon resonance (SPR) based sensor for the detection of heavy metal ions in the drinking water is designed. Silver (Ag) metal and indium tin oxide (ITO) are used for the fabrication of the SPR probe which is further modified with the coating of pyrrole and chitosan composite. The sensor works on the wavelength interrogation technique and is capable of detecting trace amounts of Cd(2+), Pb(2+), and Hg(2+) heavy metal ions in contaminated water. Four types of sensing probes are fabricated and characterised for heavy metal ions out of these pyrrole/chitosan/ITO/Ag coated probe is found to be highly sensitive among all other probes. Further, the cadmium ions bind strongly to the sensing surface than other ions and due to this the sensor is highly sensitive for Cd(2+) ions. The sensors performance is best for the low concentrations of heavy metal ions and its sensitivity decreases with the increasing concentration of heavy metal ions.

Versatile SERS sensing based on black silicon

Black Si (b-Si) with gold or silver metal coating has been shown to be an extremely effective substrate for surface-enhanced Raman scattering (SERS). Here, we demonstrate that it is also a highly versatile SERS platform, as it supports a wide range of surface functionalizations. In particular, we report the use of a molecularly imprinted polymer (MIP) coating and a hydrophobic coating on b-Si to establish two different sensing modalities. First, using a MIP layer on Au-coated b-Si, we show selective sensing of two closely related varieties of tetracycline. Second, a hydrophobic coating was used to concentrate the analyte adsorbed on gold colloidal nanoparticles, thus increasing the sensitivity of the measurement by an order of magnitude. In this experiment, Au nanoparticles and analyte were mixed just before SERS measurements and were concentrated by drop-drying on the super-hydrophobic b-Si. These approaches are promising for SERS measurements that are sensitive to the aging of bare plasmonic metal-coated substrates.

Surface-Plasmon-Resonance-Based Fiber-Optic Sensor for the Detection of Low-Density Lipoprotein

We report the fabrication and characterization of a surface plasmon resonance (SPR)-based fiber-optic sensor for the detection of low-density lipoprotein (LDL). The probe is prepared by first coating a 50-nm-thick gold film on the unclad portion of the optical fiber core and then immobilizing 4-aminothiophenol (4-ATP), followed by antiapolipoprotein B, over the 4-ATP/Au surface. Spectral interrogation technique is used for the characterization of the probe. SPR spectra are recorded for sample solutions of LDL with concentrations in the range of 0-190 mg/dl. Sensitivity of the sensor is found to be 0.18387 nm per mg/dl. Furthermore, the response time of the sensor is very small (around 2 min). The sensor can be utilized in online monitoring as well. This paper may result in the commercialization of a miniaturized low-cost reusable fast and accurate optical fiber sensor for the detection of LDL level in human blood.

Ameliorated synthetic methodology for crystalline lanthanoid–metalloporphyrin open frameworks based on a multitopic octacarboxy-porphyrin scaffold: structural, gas sorption and photophysical properties

New crystalline lanthanoid–metalloporphyrin porous frameworks [(Zn(H2O)–OCPP)Ln2(H2O)4Na2]n·solvent (Ln = Sm, Eu, Gd, Tb, and Dy) (LnMPF-1) were synthesized from an octatopic tetrakis-(3,5-dicarboxyphenyl)porphyrin building block through a synthetic approach using NaOH as a modulator to enhance the robustness of the metal–organic-framework (MOF) product and the formation of sizeable crystals. The formulated MOFs adopt a (4,8)-connected topology and are perforated by 1D tubular zigzag channels of about 1.5 nm in diameter. The frameworks possess permanent porosity and display appealing photophysical properties.

Surface plasmon resonance based fiber optic glucose biosensor

A surface plasmon resonance (SPR) based fiber optic biosensor has been fabricated and characterized for the detection of blood glucose. Optical fiber sensor was fabricated by first coating a 50 nm thick gold film on the bare core of optical fiber and then immobilizing glucose oxidase (GOx) over it. Aqueous glucose solutions of different concentrations were prepared. To mimic the blood glucose levels, the concentration of glucose solutions were kept equal to that in human blood. The refractive indices of these sample solutions were equal to that of water up to third decimal place. SPR spectra for the sensor were recorded for these glucose solutions. When the glucose comes in contact to glucose oxidase, chemical reactions take place and as a result, the refractive index of the immobilized GOx film changes, giving rise to a shift in the resonance wavelength. Unlike electrochemical sensors, the present sensor is based on optics and can be miniaturized because of optical fiber. The present study provides a different approach for blood glucose sensing and may be commercialized after optimization of certain parameters.

Surface Plasmon resonance based tapered fiber optic sensor with different taper profiles

Surface Plasmon resonance based tapered fiber optic sensor with different taper profiles is presented. Present probe design is found to be much better than the uniform core fiber optic sensor in terms of its sensitivity.

SPR Based Fiber Optic Sensor for the Detection of Vitellogenin: AnEndocrine Disruption Biomarker in Aquatic Environments

We have fabricated a fiber optic SPR biosensor for the detection of vitellogenin (Vg), an endocrine disruption biomarker in aquatic environments. The sensor was fabricated by immobilizing anti-Vg antibodies on the sensor surface. Control experiments performed on another similar protein, fetuin and on a sensing probe without the anti-Vg antibody receptor confirmed the specificity of the sensor. The limit of detection of the sensor was found to be as small as 1 ng/ml in our experimental window. The sensitivity of the sensor was 0.48 nm/(ng/ml). This sensor can be utilized for remote monitoring of the water bodies for any endocrine disruption phenomena.

Fiber optic surface plasmon resonance based ethanol sensor

A design of SPR based fiber optic ethanol biosensor is presented by using enzyme alcohol dehydrogenase and nicotinic acid. The sensing probe is fabricated with the coating of 40 nm thin film of silver metal and immobilization of alcohol dehydrogenase and nicotinic acid by gel entrapment method over unclad core of a multimode optical fiber. The SPR spectra of ethanol samples of concentrations ranging from 0 mM to 10 mM prepared in buffer have been recorded. The sensor works on the spectral interrogation technique and operates in the visible range of the spectrum. The SPR curves are blue shifted with the increasing concentration of ethanol and the sensitivity of the sensor decreases with the increasing concentration of ethanol. The sensor has many advantages such as fast response, stability, small probe size, low cost and can be used for remote/online monitoring.

Surface plasmon resonance based multi-channel and multi-analyte fiber optic sensor

Surface plasmon resonance (SPR) based fiber optic sensor has been studied for multichannel and multianalyte sensing. Simulations have been carried out for a fiber optic sensor having two sensing regions coated with silver and gold for multichannel and multianalyte sensing. The simulated results have been obtained for different combinations of refractive indices of the samples around the probes. To support simulations optical fiber SPR probes with two sensing regions coated with silver and gold have been fabricated. SPR spectra for these sensors have been recorded for aqueous sucrose solutions of varying refractive indices. The refractive index of the liquid samples around both the gold and silver coated regions was kept the same to see the potential of SPR based fiber optic multichannel sensing, while it was kept different for studies related to multianalyte sensing. Both the theoretical and experimental results match qualitatively. The SPR resonance wavelengths for gold and silver being different, these sensors can be utilized for both multichannel and multianalyte sensing.

Black-Si as a platform for sensing

The nano-textured surface of black silicon can be used as a surface-enhanced Raman scattering (SERS) substrate. Sputtered gold films showed increasing SERS sensitivity for thicknesses from 10 up to 300 nm, with sensitivity growing nonlinearly from around 50 nm until saturation at 500 nm. At 50 nm, a cross over from a discontinuous to a fully percolated film occurs as revealed by morphological and electrical measurements. The roughness of the Au coating increases due to formation of nanocrystallites of gold. Structural characterization of the black- Si needles and their surfaces revealed presence of silicon oxide and fluoride. The sharpest nano-needles had a tip curvature radius of ~10 nm. SERS recognition of analyte using molecular imprinted gels with tetracycline molecules of two different kinds is demonstrated.