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Profiling of advanced glycation end products (AGEs) is an emerging area of clinical significance for disease diagnosis and prognosis. Typically, concentrations of AGEs are estimated in laboratories by trained personnel using sophisticated equipment. Herein, a facile approach for colorimetric and fluorometric profiling of AGEs is reported for rapid and on-site analysis. The concentrations of AGE levels in plasma are estimated via changes in optical properties of polythiophenes (PTs) upon interaction with aptamers (Apts) in the presence and in the absence of AGEs. To validate the proposed approach, glyceraldehyde-derived AGEs (AGE class 1 [AGE1]), the biomarker associated with cardiovascular diseases and diabetes, are used as a model system. Colorimetric analysis yielded linear responses for AGE1 for clinically relevant concentration ranges between 1.5 and 300 μg/mL with a limit of detection (LOD) of ∼1.3 μg/mL. Subsequently, an approach utilizing PTs with four different pendant groups in conjunction with four different Apts is demonstrated for qualitative colorimetric profiling and for quantitative fluorometric profiling of up to four AGEs in clinical matrices. Principal component analysis (PCA) of fluorometric responses of AGE-spiked samples yielded distinct responses for the different AGEs tested. Thus, the proposed approach ascertains rapid profiling of spiked AGEs in plasma samples without the requirement of preanalytical processing and advanced instrumentation, thereby facilitating on-site diagnosis. Ministry of Education (MOE) The authors wish to acknowledge funding support from Tier 1, MOE -RG 82/12, and NITHM Exploratory Research grant M4081989.070.

A flow-through colorimetric assay for detection of nucleic acids in plasma is reported. The proposed assay features an array of four polyvinylidene fluoride (PVDF) membranes impregnated with cationic poly (3-alkoxy-4-methylthiophene) (PT) as an optical reporter. The sensing strategy is based on monitoring the changes in optical properties of PT, upon complexation with target nucleic acids in the presence and in the absence of their corresponding complementary peptide nucleic acids (PNAs). As a proof of concept, the proposed methodology is validated using two biomarkers; lung cancer associated microRNA (mir21) and hepatitis B virus DNA (HBV-DNA). The flow-through colorimetric assay enabled detection of mir21 and HBV-DNA in plasma without requiring tedious sample pre-treatment and clean up protocols. Colorimetric responses for mir21 and HBV-DNA were obtained at nanomolar concentrations over five orders of magnitudes (from 1 nM to 10 μM), with a limit of detection of ∼0.6 nM and ∼2 nM in DI water and plasma, respectively. A logic gate system was developed to utilize the colorimetric assay responses as inputs for discrimination of mir21 and HBV-DNA and subsequently to obtain a profile of nucleic acids in samples that exceed respective clinical threshold limits, thereby enabling rapid and point of care (POC) disease diagnosis. Furthermore, the proposed methodology can be utilized for detection of a large number of nucleic acids in plasma by extending the array of PT impregnated membranes incorporated with their corresponding complementary PNAs. Accepted version

This paper describes an approach for colorimetric detection of salivary α-amylase, one of the potential biomarkers of autonomic nervous system (ANS) activity, for enabling assessment of fatigue. The ability of α-amylase to cleave α-bonds of polysaccharides is utilized for developing a colorimetric assay. In the proposed approach, 2-chloro-4-nitrophenyl-α-d-maltotrioside as substrate releases a colored byproduct upon cleavage by salivary α-amylase. Introduction of maltose as a noncompetitive inhibitor yields desirable linear responses in the physiologically relevant concentration range (20–500 μg/mL) with a limit of detection (LOD) of 8 μg/mL (in aqueous solution). The concentrations of substrate and noncompetitive inhibitor are subsequently optimized for colorimetric detection of salivary α-amylase. A facile paper-based “strip” assay is proposed for analysis of human saliva samples with marginal interference from saliva components. The proposed assay is rapid, specific, and easy-to-implement for colorimetric detection of salivary α-amylase between 20 and 500 μg/mL. Complementary RGB (red, green, blue components) analysis offers quantitative detection with a LOD of 11 μg/mL. The two assay formats are benchmarked against the Phadebas test, a state of the art method for spectrophotometric detection of α-amylase. The reported paper-based methodology possesses a high potential for estimation of altered ANS responses toward stressors that possibly could find applications in assessment of fatigue and for monitoring onset of fatigue. Nanyang Technological University Accepted version This work is supported by Provost’s office and Institute for Sports Research (ISR), School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.

A colorimetric Al3+ sensor based on fluorescence recovery of a conjugated copolymer-ATP complex is proposed. An optimized ratio of two polythiophene (PT) monomers is utilized to synthesize copolymer (CP) that yielded maximized colorimetric response for Al3+ in deionized (DI) and tap water. The electrostatic disassembly of CP-ATP upon addition of Al3+ led to an evident visual color change. The lowest concentration of Al3+ for naked eye observation is around 4 μM, which is below the threshold levels in drinking water according to European Economic Community (EEC) standard. Besides, the proposed assay showed a similar response to Al3+ in tap water. The proposed methodology showed selective and sensitive detection for Al3+ in analytically relevant concentration ranges without involving sophisticated instrumentation, illustrating the applicability for on-site drinking water monitoring., MOE (RG 82/12); Provost Office Nanyang Technological University, Singapore