Sruthi P. Usha

Fiber optic profenofos sensor based on surface plasmon resonance technique and molecular imprinting

A successful approach for the fabrication and characterization of an optical fiber sensor for the detection of profenofos based on surface plasmon resonance (SPR) and molecular imprinting is introduced. Molecular imprinting technology is used for the creation of three dimensional binding sites having complementary shape and size of the specific template molecule over a polymer for the recognition of the same. Binding of template molecule with molecularly imprinted polymer (MIP) layer results in the change in the dielectric nature of the sensing surface (polymer) and is identified by SPR technique. Spectral interrogation method is used for the characterization of the sensing probe. The operating profenofos concentration range of the sensor is from 10(-4) to 10(-1)µg/L. A red shift of 18.7 nm in resonance wavelength is recorded for this profenofos concentration range. The maximum sensitivity of the sensor is 12.7 nm/log (µg/L) at 10(-4)µg/L profenofos concentration. Limit of detection (LOD) of the sensor is found to be 2.5×10(-6)µg/L. Selectivity measurements predict the probe highly selective for the profenofos molecule. Besides high sensitivity due to SPR technique and selectivity due to molecular imprinting, proposed sensor has numerous other advantages like immunity to electromagnetic interference, fast response, low cost and capability of online monitoring and remote sensing of analyte due to the fabrication of the probe on optical fiber.

Fabrication and Characterization of a SPR Based Fiber Optic Sensor for the Detection of Chlorine Gas Using Silver and Zinc Oxide

A fiber optic chlorine gas sensor working on surface plasmon resonance (SPR) technique fabricated using coatings of silver and zinc oxide films over unclad core of the optical fiber is reported. The sensor probe is characterized using wavelength interrogation and recording SPR spectra for different concentrations of chlorine gas around the probe. A red shift is observed in the resonance wavelength on increasing the concentration of the chlorine gas. The thickness of the zinc oxide film is optimized to achieve the maximum sensitivity of the sensor. In addition to wavelength interrogation, the sensor can also work on intensity modulation. The selectivity of the sensor towards chlorine gas is verified by carrying out measurements for different gases. The sensor has various advantages such as better sensitivity, good selectivity, reusability, fast response, low cost, capability of online monitoring and remote sensing.

Surface Plasmon Resonance-Based Fiber Optic Sensors Utilizing Molecular Imprinting

Molecular imprinting is earning worldwide attention from researchers in the field of sensing and diagnostic applications, due to its properties of inevitable specific affinity for the template molecule. The fabrication of complementary template imprints allows this technique to achieve high selectivity for the analyte to be sensed. Sensors incorporating this technique along with surface plasmon or localized surface plasmon resonance (SPR/LSPR) provide highly sensitive real time detection with quick response times. Unfolding these techniques with optical fiber provide the additional advantages of miniaturized probes with ease of handling, online monitoring and remote sensing. In this review a summary of optical fiber sensors using the combined approaches of molecularly imprinted polymer (MIP) and the SPR/LSPR technique is discussed. An overview of the fundamentals of SPR/LSPR implementation on optical fiber is provided. The review also covers the molecular imprinting technology (MIT) with its elementary study, synthesis procedures and its applications for chemical and biological anlayte detection with different sensing methods. In conclusion, we explore the advantages, challenges and the future perspectives of developing highly sensitive and selective methods for the detection of analytes utilizing MIT with the SPR/LSPR phenomenon on optical fiber platforms.

A contemporary approach for design and characterization of fiber-optic-cortisol sensor tailoring LMR and ZnO/PPY molecularly imprinted film

A fiber optic salivary cortisol sensor using a contemporary approach of lossy mode resonance and molecular imprinting of nanocomposites of zinc oxide (ZnO) and polypyrrole (PPY) is structured and depicted for the concentration range of 0-10-6g/ml of cortisol prepared in artificial saliva. Components of polymer preparation and the nanocomposite of polymer with ZnO are optimized for realizing the molecular imprinted layer of the sensor. Nanocomposite having 20% of ZnO in PPY is found to give highest sensitivity of the sensor. The sensor reports the best limit of detection ever reported with better stability, repeatability and response time. Lossy mode resonance based salivary cortisol sensor using nanocomposite molecular imprinted layer reported first time boosts the specificity of the sensor. The implementation of sensor over optical fiber adds up other advantages such as real time and online monitoring along with remote sensing abilities which makes the sensor usable for nonintrusive clinical applications.

Zinc oxide thin film/nanorods based lossy mode resonance hydrogen sulphide gas sensor

We report a fiber optic hydrogen sulfide gas sensor based on lossy mode resonance utilizing a coating of zinc oxide thin film along with nanorods over the unclad core of the fiber. The sensor is characterized in terms of peak absorbance wavelength determined from the recorded lossy mode resonance spectra for different concentrations of the hydrogen sulfide gas. To achieve the maximum sensitivity of the sensor, the growing period of the nanorods is optimized. It is found that the sensitivity of the sensor depends on the concentration of the gas. Further, the sensor is best suited for low concentrations (less than 60 ppm) of the gas. Experiments are also performed on the probe fabricated with zinc oxide nanorods grown over the unclad portion of the fiber. On comparison, it is found that the probe with layers of zinc oxide thin film and its nanorods is more sensitive than the probe that has layer of nanorods only. This is because of the large active surface area available in the probe fabricated with zinc oxide thin film and its nanorods. In addition, the probe with zinc oxide thin film and its nanorods is highly selective to hydrogen sulfide gas.

Highly sensitive and selective erythromycin nanosensor employing fiber optic SPR/ERY imprinted nanostructure: Application in milk and honey

An erythromycin (ERY) detection method is proposed using the fiber optic core decorated with the coatings of silver and an over layer of ERY imprinted nanoparticles. Synthesis of ERY imprinted nanoparticles is carried out using miniemulsion method. The operating range of the sensor is observed to be from 1.62×10-3 to 100µM while the sensor possesses the linear response for ERY concentration range from 0.1 to 5µM. The sensing method shows a maximum sensitivity of 205nm/µM near ERY concentration of 0.01µM. The detection limit and the quantification limit of the sensor are found to be 1.62×10-3µM and 6.14×10-3µM, respectively. The sensors applicability in real samples is also examined and is found to be in good agreement for the industrial application. The sensor possesses numerous advantages like fast response time (<15s), simple, low cost, highly selective along with abilities towards online monitoring and remote sensing of analyte.

A lossy mode resonance-based fiber optic hydrogen gas sensor for room temperature using coatings of ITO thin film and nanoparticles

In this article, the idea of employing lossy mode resonances (LMR) concertedly for gas sensing along with the reversible interaction of metal oxides with gases has been investigated. Fabrication and characterization of a LMR-based fiber optic probe with successive coatings of indium-tin oxide (ITO) film and nanoparticles over the unclad core of the fiber have been carried out for the detection of hydrogen gas (H2). The results have been compared with the probes having individual coatings of ITO thin film and nanoparticles. For calibrating and comparing, the wavelength interrogative spectra have been recorded for varying concentrations of H2 gas exploiting the sensor probes. A red shift of the spectrum has been observed with the increase in the concentration of the gas. The results uphold the fact that the LMR-based sensor with both thin film and nanoparticles layer has better sensitivity to H2 gas than the probes with the layer of either nanoparticles or thin film. A collective study on the three probes for different gases has predicted a maximum level of sensitivity for the probe with layers of thin film and nanoparticles along with the high selectivity and repeatability of the results for H2 gas. In addition to high sensitivity and selectivity, the proposed sensor can be used for online monitoring and remote sensing of the gas because of the fabrication of the probe on the optical fiber.

FO-SPR based dextrose sensor using Ag/ZnO nanorods/GOx for insulinoma detection.

In this piece of work, a fiber optic sensor has been fabricated and characterized using surface plasmon resonance for dextrose sensing. The concentration range used in this study is for diagnosing the cases of hypoglycaemia especially in suppression tests of insulinoma. Insulinoma is a medical case in which the person is recognized being hypoglycaemic with the blood dextrose level falling down to 2.2mM or less. Thus, the sensor has been characterized for the dextrose concentration range of 0 mM-10mM including the cases of normal blood dextrose range. Coatings of silver layer and zinc oxide nanorods have been carried out on the bare core fiber with a dual role of zinc oxide followed by immobilization of glucose oxidase. A three stage optimization procedure has been adopted for the best performance of the sensor. Absorbance spectra have been plotted and peak absorbance wavelengths have been extracted for each concentration chosen along with the sensitivities. The results have been made conclusive with control experiments. The probe has also been tested on sample having blood serum to check the reliability of the sensor. The sensor shows better selectivity and response time along with its real time applications, online monitoring, remote sensing and reusability.

Urinary p-cresol diagnosis using nanocomposite of ZnO/MoS2 and molecular imprinted polymer on optical fiber based lossy mode resonance sensor

A lossy mode resonance (LMR) based sensor for urinary p-cresol testing on optical fiber substrate is developed. The sensor probe fabrication includes dip coating of nanocomposite layer of zinc oxide and molybdenum sulphide (ZnO/MoS2) over unclad core of optical fiber as the transducer layer followed by the layer of molecular imprinted polymer (MIP) as the recognition medium. The addition of molybdenum sulphide in the transducer layer increases the absorption of light in the medium which enhances the LMR properties of zinc oxide thereby increasing the conductivity and hence the sensitivity of the sensor. The sensor probe is characterized for p-cresol concentration range from 0µM (reference sample) to 1000µM in artificially prepared urine. Optimizations of various probe fabrication parameters are carried to bring out the sensors optimal performance with a sensitivity of 11.86nm/µM and 28nM as the limit of detection (LOD). A two-order improvement in LOD is obtained as compared to the recently reported p-cresol sensor. The proposed sensor possesses a response time of 15s which is 8 times better than that reported in the literature utilizing electrochemical method. Its response time is also better than the p-cresol sensor currently available in the market for the medical field. Thus, with a fast response, significant stability and repeatability, the proposed sensor holds practical implementation possibilities in the medical field. Further, the realization of sensor probe over optical fiber substrate adds remote sensing and online monitoring feasibilities.

Localized surface plasmon resonance–based fiber-optic sensor for the detection of triacylglycerides using silver nanoparticles

Abstract. A label-free technique for the detection of triacylglycerides by a localized surface plasmon resonance (LSPR)–based biosensor is demonstrated. An LSPR-based fiber-optic sensor probe is fabricated by immobilizing lipase enzyme on silver nanoparticles (Ag-NPs) coated on an unclad segment of a plastic clad optical fiber. The size and shape of nanoparticles were characterized by high-resolution transmission electron microscopy and UV–visible spectroscopy. The peak absorbance wavelength changes with concentration of triacylglycerides surrounding the sensor probe, and sensitivity is estimated from shift in the peak absorbance wavelength as a function of concentration. The fabricated sensor was characterized for the concentration of triacylglyceride solution in the range 0 to 7 mM. The sensor shows the best sensitivity at a temperature of 37°C and pH 7.4 of the triacylglycerides emulsion with a response time of 40 s. A sensitivity of 28.5  nm/mM of triacylglyceride solution is obtained with a limit of detection of 0.016 mM in the entire range of triacylglycerides. This compact biosensor shows good selectivity, stability, and reproducibility in the entire physiological range of triacylglycerides and is well-suited to real-time online monitoring and remote sensing.