Dr. Ruchi Gupta Profile

Dr. Ruchi Gupta

at Univ of Birmingham

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Publications (2)

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Proceedings Article | 1 April 2020 Paper

Aqueous photochemistry for the fabrication of grating sensors in hydrogels

Anil Kumar Pal, Nicholas Goddard, Ruchi Gupta

Proceedings Volume 11367, 1136702 (2020) https://doi.org/10.1117/12.2564248

KEYWORDS: Diffraction gratings, Diffraction, Refractive index, Absorbance, Sensors, Waveguides

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A photofunctionalisable hydrogel based on copolymers of a nitroveratryl chloroformate derivative with acrylamide has been developed that permits the uncaging of amine groups on exposure to patterns of light at 405 nm using a watersoluble thioxanthone sensitizer. Hydrogel films of 3, 35 and 100 μm thickness were fabricated to use as leaky waveguide and grating sensors. The smallest feature sizes produced in 35 and 100 μm thick films were 21.6 and 43.2 μm respectively, limited by the depth of field of the digital projector. It was found that essentially complete deprotection could be obtained in ~2 minutes. The two thicker hydrogel films were used to create amplitude and phase gratings, while the thinnest film was used as a leaky waveguide to investigate the porosity of the films and monitor immobilization of protein using a PEG linker. The amplitude grating formed by reacting the uncaged amines with fluorescein isothiocyanate was shown to act as a pH sensor with resolution 0.0325 pH units. Protein immobilization using glutaraldehyde as a linker to create a phase grating was attempted, which gave a strong signal with glutaraldehyde but no subsequent signal with BSA. Investigation with a thin film acting as a leaky waveguide showed that glutaraldehyde significantly reduces the porosity of the film to high molecular mass species. Finally, leaky waveguiding was used to monitor protein immobilization using an amine-reactive PEG linker, showing that selective immobilization occurred in the exposed regions of the film without affecting the sensitivity of the film to bulk index changes.

Proceedings Article | 21 February 2020 Presentation + Paper

Biosensor for determining average iron content of ferritin by measuring its optical dispersion

Ruchi Gupta, Nasser Alamrani, Gillian Greenway, Nicole Pamme, Nicholas Goddard

Proceedings Volume 11235, 112350M (2020) https://doi.org/10.1117/12.2542162

KEYWORDS: Iron, Proteins, Waveguides, Dispersion, Biosensors, Chemical species, Refractive index, Coating, Point-of-care devices, Visible radiation

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Average iron content of ferritin has a potential to serve as a biomarker for early identification of high-risk trauma patients at point-of-care (PoC). Appropriate therapies can then be administered to reduce morbidity and mortality. Currently, protein and iron levels are measured separately using enzyme-linked immunosorbent assay (ELISA) and UV or atomic absorption spectroscopy (AAS) respectively, but the use of two completely different methods adds to the complexity and analysis time of the combined measurement. As a result, these methods are unsuitable for PoC analysis. To address this gap, we report a biosensor for measuring the average iron content of ferritin in a single step. The biosensor was based on a dye-doped leaky waveguide (LW), which operates in the entire visible wavelength range, and hence allowed the measurement of differences in the optical dispersion of ferritin and apoferritin to determine the average iron content of the protein. The LW biosensor comprised a 1.54 micron thick mesoporous chitosan slab waveguide with immobilized antibodies against ferritin/ apoferritin to measure the optical dispersion of 110 nM protein. Based on the baseline noise, the limit of detection for this method is ~700 pM for ferritin/ apoferritin. The biosensor has a significant potential for PoC measurement of the average iron content of serum ferritin and, in future, the total protein cencentration.

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