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Although CRISPR-based nucleic acid detection has great potential in point-of-care testing due to its simplicity, it has been rarely integrated into paper-based analytical devices (PADs), which are attractive platforms to simplify assays. This work introduces a CRISPR-assisted nucleic acid quantification approach integrated into a PAD with signal readout by a personal glucose meter (PGM). Retention of magnetic beads by filter paper and pre-deposition of all required reagents by freeze-drying stabilized with trehalose enabled the indirect quantification of human papilloma virus (HPV) DNA through a PGM readout without complicated user intervention and complex reagent handling. The calculated limit of detection was 57 pM, which is comparable with other amplification-free CRISPR-based assays detecting nucleic acids. The fully integrated device exhibited good storage stability for up to 4 weeks, suggesting its applicability toward practical point-of-care nucleic acid quantification.

The wide spread of smartphones and QR codes for various end-user applications has had an impact beyond traditional fields of use, recently also reaching point-of-care testing (POCT). This work presents the integration of QR code recognition into paper-based analytical devices (PADs) with "distance-based" colorimetric signalling, resulting in semiquantitative readout fully relying on straightforward barcode reader solutions. PADs consist of an array of QR codes arranged in series inside a paperfluidic channel. A mask dye concept has been developed, which enables utilisation of colour changing indicators by initially hiding QR codes. The colour change of the indicator induced by the presence of an analyte of interest results in gradual unmasking of QR codes, which become recognisable by the smartphone barcode reader app. To reproducibly fabricate devices, all fabrication steps were performed by commercial desktop solid ink and inkjet printing. The QR code masking function was optimised by controlling the amount of printed mask dye through adjusting the opacity of printing patterns during the inkjet deposition process. For proof-of-concept, a model assay in the form of colorimetric copper ion (Cu2+) detection in the concentration range of 0.4 mM to 3.2 mM was evaluated. Consistent results independent of the smartphone model and environmental light condition were achieved with a free barcode reader app. To the best of our knowledge, this work is the first demonstration of a semiquantitative assay approach fully relying on QR code readout without digital colour analysis, customised app or hardware modification.

Although the determination of calcium ions (Ca 2+ ) is of high importance to monitor water hardness, currently available devices for on-site analysis suffer from a lack of user-friendliness and sensitivity. This work demonstrates fully inkjet-printed and low-cost microfluidic paper-based analytical devices (μPADs) for the simple naked-eye colorimetric determination of calcium ions (Ca 2+ ) in drinking and tap water samples. The quantification of Ca 2+ relies on visual readout of the length of a colour-changed detection channel modified with ionophore-doped ion-selective optode nanospheres (nano-optodes), eliminating the requirement of a scanner or a camera. All fabrication steps for deposition of assay reagents have been performed by means of a simple desktop thermal inkjet printer, which is expected to contribute to highly batch-to-batch reproducible device preparation. The detectable Ca 2+ concentrations between 0.05 mmol L -1 and 5 mmol L -1 cover the range recommended by the International Organization for Standardization (0.05-2.5 mmol L -1 ) and the World Health Organization (WHO) guideline for Ca 2+ quantification in drinking water (less than 5 mmol L -1 ). The lowest concentration of Ca 2+ detectable by the naked eye was found to be 0.05 mmol L -1 , which is below the value achieved with previously reported paper-based devices. μPAD quantified Ca 2+ concentrations in tap or drinking waters were within 15% error of the results obtained with a classical complexometric titration. Hence, distance-based μPADs relying on nano-optodes are sensitive and reproducible tools for equipment-free on-site assaying of Ca 2+ in real samples.

Temperature-responsive polymers incorporating molecular-recognition sites were developed as stationary phases for high-performance liquid chromatography (HPLC). The grafted stationary phases consisted of functional copolymers composed of N-isopropylacrylamide (NIPAAm) and N-acryloyl aromatic amino acid methyl esters, i.e., phenylalanine and tryptophan methyl esters (Phe-OMe and Trp-OMe). Three novel temperature-responsive polymers, P(NIPAAm-co-Phe-OMe5), P(NIPAAm-co-Phe-OMe10), and P(NIPAAm-co-Trp-OMe5), were synthesized. These copolymers exhibited a reversible hydrophilic/hydrophobic phase transition at their lower critical solution temperatures (LCSTs). The polymers were grafted onto aminopropyl silica using an activated ester-amine coupling method, and were packed into a stainless steel column, which was connected to an HPLC system. Temperature-responsive chromatography was conducted using water as the sole mobile phase. More hydrophobic analytes were retained longer, and the retention times of aromatic steroids and aromatic amino acids were dramatically increased. This indicated that π-π interactions occurred between the phenyl or indole moieties of phenylalanine or tryptophan, respectively, and the aromatic compounds. Furthermore, the retention times of compounds with hydrogen bond acceptors were higher with P(NIPAAm-co-Trp-OMe5), which contained indole as a hydrogen bond donor, than with P(NIPAAm-co-Phe-OMe5). This indicated that hydrogen bonding occurred between the stationary phase and the analytes. These results indicate that hydrophobic, π-π, and hydrogen bonding interactions all affected the separation mode of the temperature-responsive chromatography, and led to selective separation with molecular recognition. Both temperature-response and molecular recognition characteristics are present in the proposed separation system that utilizes a temperature-responsive polymer bearing aromatic amino acid derivatives.

This paper presents the preparation and characterization of a single-excitation, dual-emission ratiometric optical Li(+)-sensing device using a newly designed and synthesized highly Li(+)-selective fluoroionophore (KBL-01) carrying 14-crown-4 ether with tetramethyl and benzene blocking subunits as Li(+)-binding site and boron-dipyrromethene as fluorophore. The indicator dye was covalently immobilized on the surface of a porous glass support having a large internal surface area using a silane-coupling agent. The resulting Li(+)-selective glass optode shows dual fluorescence emission response in pseudo-serum at varying Li(+) concentrations, allowing ratiometric signal processing. The obtained signal is independent of the presence of possibly interfering cations (Na(+), K(+), Mg(2+) and Ca(2+)) and pH. The sensor response was found to be reversible within the Li(+) concentration range from 10(-4) to 10(-1) M, and showed good repeatability and light stability. The plots of the ratiometric signal versus the Li(+) concentrations in spiked real human serum go along with the response curve in pseudo-serum. These results indicate that the novel Li(+)-selective glass optode can be employed as a Li(+)-sensing device with high durability, sensitivity and accuracy for medical analyses.