As glucose biosensors play an important role in glycemic control, which can prevent the diabetic complications, the development of a glucose sensing platform is still in needed. Herein, the first proposal on the in-house fabricated paper-based screen-printed ionic liquid/graphene electrode (SPIL-GE) modified with MXene (Ti₃C₂T_x), prussian blue (PB), glucose oxidase (GOx), and Nafion is reported. The concentration of PB/Ti₃C₂T_x was optimized and the optimal detection potential of PB/Ti₃C₂T_x/GOx/Nafion/SPIL-GE is −0.05 V. The performance of PB/Ti₃C₂T_x/GOx/Nafion modified SPIL-GE was characterized by cyclic voltammetry and chronoamperometry technique. This paper-based platform integrated with nanomaterial composites were realized for glucose in the range of 0.0–15.0 mM with the correlation coefficient R² = 0.9937. The limit of detection method and limit of quantification were 24.5 μM and 81.7 μM, respectively. In the method comparison, this PB/Ti₃C₂T_x/GOx/Nafion/SPIL-GE exhibits a good correlation with the reference hexokinase method. This novel glucose sensing platform can potentially be used for the good practice to enhance the sensitivity and open the opportunity to develop paper-based electroanalytical devices.

This paper proposes a combined strategy of using paper-based competitive immunochromatography and a near field communication (NFC) tag for wireless cotinine determination. The glucose oxidase labeled cotinine antibody specifically binds free cotinine in a sample, whereas the unoccupied antibody attached to BSA-cotinine at the test line on a lateral flow strip. The glucose oxidase on the strip and an assistant pad in the presence of glucose generated H₂O₂ and imposed the Ag oxidation on the modified electrode. This enabled monitoring of immunoreaction by either electrochemical measurement or wireless detection. Wireless sensing was realized for cotinine in the range of 100–1000 ng/mL (R² = 0.96) in PBS medium. Undiluted urine samples from non-smokers exhibited an Ag-oxidation rate three times higher than the smoker’s urine samples. For 1:8 diluted urine samples (smokers), the proposed paper-based competitive immunochromatography coupled with an enzyme-modified electrode differentiated positive and negative samples and exhibited cotinine discrimination at levels higher than 12 ng/mL. This novel sensing platform can potentially be combined with a smartphone as a reader unit.

Commercially available sorbent materials for solid-phase extraction are widely used in analytical laboratories. However, non-selective binding is a major obstacle for sample analysis. To overcome this problem, molecularly imprinted polymers (MIPs) were used as selective adsorbent materials prior to determining target analysts. In this study, the use of non-covalent molecularly imprinted polymers (MIPs) for cotinine adsorption on a paper-based scaffold was studied. Fiberglass paper was used as a paper scaffold for cotinine-selective MIP adsorption with the use of 0.5% agarose gel. The effects of salt, pH, sample matrix, and solvent on the cotinine adsorption and extraction process were investigated. Under optimal conditions, the adsorption isotherm of synthesized MIPs increased to 125.41 µg/g, whereas the maximum adsorption isotherm of non-imprinted polymers (NIPs) was stable at 42.86 µg/g. The ability of the MIP paper scaffold to absorb cotinine in water medium was approximately 1.8–2.8-fold higher than that of the NIP scaffold. From Scatchard analysis, two dissociation constants of MIPs were calculated to be 2.56 and 27.03 µM. Nicotine, myosmine, and N-nitrosonornicotine were used for selectivity testing, and the calculated selectivity factor of cotinine to nicotine, myosmine, and N-nitrosonornicotine was 1.56, 2.69, and 2.05, respectively. Overall, the MIP paper scaffold is promising for simple onsite sampling of cotinine and can be used to assess tobacco smoke exposure.