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Gel-based, 3D visual and colorimetric detection of a skin cancer biomarker using immunodiagnostic microneedles

Lookup NU author(s): Dr Ashwin Sivaharan, Dr Wing Man Lau, Dr Keng Wooi Ng



This is the authors' accepted manuscript of a conference proceedings (inc. abstract) that has been published in its final definitive form by Academy of Pharmaceutical Sciences, 2019.

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Microneedle biosensors can be inserted into superficial skin to facilitate minimally invasive, biopsy-free skin biomarker profiling for disease diagnosis [1, 2]. To this end, a facile and low-resource method to reliably extract and detect skin biomarkers using an immunodiagnostic microneedle device (iMN) is desirable. We have previously reported a paper-based, 2-dimensional visual and colorimetric assay with an iMN [1]. Here, we demonstrate proof-of-concept for a gel-based, 3-dimensional visual and colorimetric assay to detect a skin melanoma biomarker (S100B) with the iMN. Based on a miniaturised sandwich enzyme-linked immunosorbent assay (ELISA), the iMN was fabricated from polylactic acid and surface-functionalised with a capture antibody recognising human S100B, bovine serum albumin (negative control) or a horseradish peroxidase (HRP)-labelled detection antibody (HRP-ab) as positive control [1]. Following incubation of the iMN with a S100B solution in vitro, captured S100B was detected with the HRP-ab. The chromogenic substrate comprised o-phenylenediamine (OPD) in a thermoreversible poloxamer 407 hydrogel (25% w/w), which was to be converted into colour signals by HRP-ab. The iMN was immersed in the cold OPD-poloxamer solution, which was warmed rapidly to induce instantaneous gellation around the microneedles. Colour development in the hydrogel around the microneedles was visualised by light microscopy. The hydrogel transitioned into a sol upon cooling. The absorbance of the sol was determined by UV/Vis spectrophotometry (450 nm) to quantify the signal. The thermoreversible sol-gel transition of the OPD-poloxamer hydrogel was exploited to enable signal visualisation in the gel, followed by signal quantification in the sol. The gel retarded the diffusion of the colour signal, allowing 3-dimensional signal visualisation across the entire microneedle surface with clear signal separation from one microneedle to another (Figure 1A). The observed intensity of the visualised signal corroborated the absorbance measured in the corresponding sol (Figure 1B). Signal visualisation was also demonstrated with a multiplexed iMN (Figure 1C). However, signal quantification with multiplexed iMN requires further development. The gel-based detection method presents a promising solution for facile and low-resource detection of skin biomarkers with iMN.

Publication metadata

Author(s): Sivaharan AJ, Lau WM, Ng KW

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: 10th APS International PharmSci Conference

Year of Conference: 2019

Acceptance date: 08/07/2019

Date deposited: 17/12/2019

Publisher: Academy of Pharmaceutical Sciences