Pabitra Nath

Evanescent Wave Coupled Spectroscopic Sensing Using Smartphone

This letter demonstrates a technique that utilizes the camera of a smartphone for evanescent wave coupled spectroscopic sensing. Using simple optical components, the camera of the smartphone is converted into a highly resolved spectrometer (0.305 nm per pixel), and using a right-angled glass prism, the evanescent field of the internally reflected light signal from a broadband optical source is allowed to interact with the external medium. The primary advantages of the proposed sensing technique are its compactness, portability, and cost-efficiency.

Smartphone based LSPR sensing platform for bio-conjugation detection and quantification

We report here the working of a localized surface plasmon resonance (LSPR) sensor using the camera of a smartphone. Integrating light weight and simple laboratory optical components with the camera module of the phone, we first designed a visible spectrophotometer with a pixel resolution of 0.336 nm per pixel. The LSPR peak absorption wavelength shift due to size variation of gold nanoparticles (AuNPs) and analyte (protein and enzyme) conjugation with AuNPs have been successfully recorded by our smartphone spectrophotometer. The shift in LSPR peak absorption wavelength can be correlated with the size of the AuNPs and concentration of biomolecules attached to it. The limit of detection (LOD) of the designed sensor for quantification of BSA protein and trypsin enzyme was estimated to be 19.2 μg mL−1 (equivalent to 0.28 μM) and 25.7 μg mL−1 (equivalent to 1.10 μM) respectively. We compare the results with a laboratory grade standard UV-VIS spectrophotometer and observe high reliability of our designed sensor. Owing to its compact size, simple optics design and involvement of low-cost optical components we envision that the proposed sensing system could emerge as an alternative inexpensive handheld LSPR sensing tool that can be suitable for different in-field applications.

Water turbidity sensing using a smartphone

This paper demonstrates a rapid, cost-effective and field-portable smartphone based turbidimeter that measures turbidity of water samples collected from different natural water resources and in drinking water. The working of the designed sensor is based on a Mie-scattering principle where suspended micro (μ-) particles in water medium scatter a strong light signal along the normal direction of the incoming light signal, which can be detected by an infra-red (IR) proximity sensor embedded in the smartphone. Two freely available android applications were used to measure the irradiance of the scattered flux and analyse the turbidity of the medium. With the designed sensor, water turbidity variation as low as 0.1 NTU can be measured accurately in the turbidity value ranging from 0 to 400 NTU. The sensor responses for these ranges of turbid media are found to be linear. A high repeatability in the sensor characteristics is also been observed. The optics design involved for the development of the proposed smartphone turbidimeter is simple and is robust in operation. The designed sensing technique could emerge as a truly portable, user-friendly and inexpensive turbidity sensing tool that would be useful for different in-field applications.

Ground and river water quality monitoring using a smartphone-based pH sensor

We report here the working of a compact and handheld smartphone-based pH sensor for monitoring of ground and river water quality. Using simple laboratory optical components and the camera of the smartphone, we develop a compact spectrophotometer which is operational in the wavelength range of 400-700 nm and having spectral resolution of 0.305 nm/pixel for our equipment. The sensor measures variations in optical absorption band of pH sensitive dye sample in different pH solutions. The transmission image spectra through a transmission grating gets captured by the smartphone, and subsequently converted into intensity vs. wavelengths. Using the designed sensor, we measure water quality of ground water and river water from different locations in Assam and the results are found to be reliable when compared with the standard spectrophotometer tool. The overall cost involved for development of the sensor is relatively low. We envision that the designed sensing technique could emerge as an inexpensive, compact and...

Dye-Assisted pH Sensing Using a Smartphone

We report the working of a smartphone-based optical sensor for the measurement of pH level of colorless aqueous media. By integrating readily available laboratory optical components to the camera of the smartphone, we convert the smartphone into a visible spectrophotometer with spectral resolution of 0.345 nm/pixel. Evanescent light signal from the designed optical sensing setup is allowed to interact with a pH sensitive dye sample. The transmitted light signal from the sensing region is then captured by the camera of the smartphone in the form of modulated visible image spectrum. The designed sensor can detect change in pH level of medium with a resolution of 0.12 pH unit within range of 6-8 pH unit. We evaluate the repeatability of our sensor for eight consecutive trials and obtained a standard deviation

Periodically Varying Height in Metal Nano-pillars for Enhanced Generation of Localized Surface Plasmon Field

\sim 0.015

Smartphone-based platform optical setup measuring π/256 optical phase difference in an interference process

in the transmission intensity within range of 6-8 pH units. We envision that our designed sensing technique could emerge as a low cost, portable, and robust pH sensor that has the ability to measure pH level of colorless aqueous medium with good accuracy and repeatability.

All Fiber-Optic Sensor for Monitoring Pressure Fluctuations in ON/OFF State

Localized surface plasmon resonance (LSPR) field condition study in metal nanostructure is important for different fields of applications which include chemical and bio-sensing investigations and in surface-enhanced Raman scattering (SERS)-based sensing investigations. Generally, sharp metal nano-tips, metal nano-colloids, nano-pillars and other sharp structures were used to generate different magnitudes of enhanced LSPR conditions, and all such structures usually provide tightly bound LSPR field conditions. In this paper, we demonstrate that with periodically varying height in metal nano-pillars, enhanced LSPR field condition can also be obtained and the enhancement scale of the generated field are found to be more than that of the uniformly structured metal nano-pillars. Different parameters which govern the enhancement factor for LSPR field condition have been thoroughly studied here. Since, periodic pattern of nano-pillars can be fabricated using lithographic tool such as e-beam lithography or focus-ion beam lithography, we envision that our simulation results would be useful in getting desired structure of the proposed nano-pillars for which it provides enhanced LSPR field condition as compared to uniformly structured metal nano-pillars.

Protein, enzyme and carbohydrate quantification using smartphone through colorimetric digitization technique

Utilizing the camera of a smartphone and simple laboratory optical components, we demonstrate an optical technique that measures an optical phase difference (OPD) of π/256 in an interference process. We develop a compact optical setup for viewing circular interference fringe patterns through the camera of the smartphone. By introducing OPD between the interfering beams, variation in fringe pattern is recorded using the smartphone camera. We envision that the proposed optical setup could emerge as an ultrasensitive optical tool for measurement of inclination of a given surface.

Fiber-Optic Volumetric Sensor Based on Beer-Lambert Principle

We report a simple, cost-efficient fiber-optic sensor for monitoring pressure fluctuations in ON/OFF state. The working principle of the proposed sensor is based on light intensity modulation of a reflected signal when external pressure fluctuations cause coupling optical signal variation between two multimode optical fibers placed side by side in front of a plane reflecting mirror attached on a pressure-sensitive diaphragm. The proposed sensing technique is found to be suitable for monitoring both periodic and nonperiodic forms of pressure variations in ON/OFF state. With our proposed sensor design, pressure variation as small as 1.5×10-5 N/cm2 can be measured with accuracy and repeatability.