An In-Vitro Optical Sensor Designed to Estimate Glycated Hemoglobin Levels.

The purpose of this research was to design an optical sensor for evaluating glycated hemoglobin (HbA1c) percentages in hemoglobin. The A1c sensors available in the market use invasive methods, while our device offers the possibility of non-invasive monitoring of HbA1c levels in diabetic patients. A prototype is assembled using two light emitting diodes with peak emission wavelengths of 535 nm and 593 nm, a photodiode, and a microcontroller. The proposed sensor measures the transmitted intensity in the form of an output voltage. We devise an approach to estimate the percentage of HbA1c in hemoglobin for a given solution. This estimation is based on the relative change in absorbance due to change in path length and molar absorption coefficients of hemoglobin and HbA1c, at the two wavelengths. We calculate the molar absorption coefficient of HbA1c at 535 nm and 593 nm wavelengths using the sensor, which is performed by a multiple variable regression analysis algorithm fed through the microcontroller. Specifically, the sensor output voltage with respect to the sample concentration is fitted to an exponentially decaying equation model. We used a commercial chemical assay called Control FD Glycohemoglobin A1c with known percentage HbA1c levels to verify our device measurements.

Vertically grown zinc oxide nanorods functionalized with ferric oxide for in vivo and non-enzymatic glucose detection.

An enzyme-free glucose sensor based on vertically grown zinc oxide nanorods (NRs) functionalized with ferric oxide (Fe2O3) is investigated. The well-aligned and high density ZnO NRs were synthesized on an FTO/glass substrate by a sol-gel and hydrothermal growth method. A dip-coating technique was utilized to modify the surface of the as-grown ZnO NRs with Fe2O3. The immobilized surface was coated with a layer of nafion membrane. The fabricated glucose sensor was characterized amperometrically at room temperature using three electrodes stationed in the phosphate buffer solution, where ZnO NRs/Fe2O3/nafion membrane was the sensing or working electrode, and platinum plate and silver/silver chloride were used as the counter and reference electrodes, respectively. The proposed non-enzymatic and modified glucose sensor exhibited a high sensitivity in the order of 0.052 µA cm-2 (mg/dL)-1, a lower detection limit of around 0.95 mmol L-1, a sharp and fast response time of ∼1 s, and a linear response to changes in glucose concentrations from 100-400 mg dL-1. The linear amperometric response of the sensor covers the physiological and clinical interest of glucose levels for diabetic patients. The device continues to function accurately after multiple measurements with a good reproducibility. The proposed glucose sensor is expected to be used clinically for in vivo monitoring of glucose.

Spectroscopy of shallow InAs/InP quantum wire nanostructures.

A comprehensive investigation of the optical properties of InAs/InP(001) quantum wires (QWrs) and their parent quantum well system formed by the deposition of 4 ML (monolayers) of InAs on InP is carried out by means of temperature dependent photoluminescence (PL) and Fourier transform infrared spectroscopy. Unusual two-branch switching of the excitonic PL band maxima is revealed in the temperature dependence for both wires and wells. This is interpreted in terms of the thermal activation of excitonic ground states of the confined nanostructures. Strong modification of the absorbance line shape leading to the appearance of flat spectral regions in the room temperature spectrum of a QWr sample is interpreted in terms of thermally induced change of the dimensionality: from 1D to anisotropic 2D. This change of dimensionality is detected also in the polarized absorbance measurements through the disappearance or significant reduction of the polarization anisotropy in the regions of the hh1-e1 (hh: heavy hole; e: electron) and lh1-e1 (lh: light hole) transitions in QWrs.