Point-of-care paper-based analytical device for potentiometric detection of myoglobin as a cardiovascular disease biomarker

One of the cardiac biomarkers, myoglobin (Mb), is important in the rapid identification of cardio-vascular disorders. Therefore, point-of-care monitoring is essential. Pursuing this goal, a robust, reliable, and affordable paper-based analytical apparatus for potentiometric sensing has been developed and characterized. The molecular imprint technique was used to create a customized biomimetic antibody for myoglobin (Mb) on the surface of carboxylated multiwalled carbon nanotubes (MWCNT-COOH). This was accomplished by attaching Mb to carboxylated MWCNTs' surfaces and then filling the empty spaces through the mild polymerization of acrylamide in N,N-methylenebisacrylamide and ammonium persulphate. The modification of the MWCNTs' surface was verified by SEM and FTIR analysis. A hydrophobic paper substrate coated with fluorinated alkyl silane (CF₃(CF₂)₇CH₂CH₂SiCl₃, CF¹⁰) has been coupled with a printed all-solid-state Ag/AgCl reference electrode. The presented sensors showed a linear range of 5.0 × 10^-8 to 1.0 × 10^-4 M with a potentiometric slope of -57.1 ± 0.3 mV decade^-1 (R² = 0.9998) and a detection limit of 28 nM at pH 4. Compared to creatinine, sucrose, fructose, galactose, sodium glutamate, thiamine, alanine, ammonium, uric acid, albumin, glutamine, guanine, troponine T, and glucose, the sensor showed good selectivity for Mb. It demonstrated a good recovery for the detection of Mb in several fake serum samples (93.0-103.3%), with an average relative standard deviation of 4.5%. The current approach might be viewed as a potentially fruitful analytical tool for obtaining disposable, cost-effective paper-based potentiometric sensing devices. These types of analytical devices can be potentially manufacturable at large scales in clinical analysis.

New Potentiometric Screen-Printed Platforms Modified with Reduced Graphene Oxide and Based on Man-Made Imprinted Receptors for Caffeine Assessment

Caffeine is a psychoactive drug that is administered as a class II psychotropic substance. It is also considered a component of analgesics and cold medicines. Excessive intake of caffeine may lead to severe health damage or drug addiction problems. The assessment of normal caffeine consumption from abusive use is not conclusive, and the cut-off value for biological samples has not been established. Herein, new cost-effective and robust all-solid-state platforms based on potentiometric transduction were fabricated and successfully utilized for caffeine assessment. The platforms were modified with reduced graphene oxide (rGO). Tailored caffeine-imprinted polymeric beads (MIPs) based on methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were prepared, characterized, and used as recognition receptors in the presented potentiometric sensing devices. In 50 mM MES buffer, the sensors exhibited a slope response of 51.2 ± 0.9 mV/decade (n = 6, R2 = 0.997) over the linear range of 4.5 × 10−6−1.0 × 10−3 M with a detection limit of 3.0 × 10−6 M. They exhibited fast detection of caffeinium ions with less than 5 s response time (<5 s). The behavior of the presented sensors towards caffeinium ions over many common organic and inorganic cations was evaluated using the modified separate solution method (MSSM). Inter-day and intra-day precision for the presented analytical device was also evaluated. Successful applications of the presented caffeine sensors for caffeine determination in commercial tea and coffee and different pharmaceutical formulations were carried out. The data obtained were compared with those obtained by the standard liquid chromatographic approach. The presented analytical device can be considered an attractive tool for caffeine determination because of its affordability and vast availability, particularly when combined with potentiometric detection.