Glycated hemoglobin (HbA1c), one of the many variants of hemoglobin (Hb), serves as a standard biomarker of diabetes, as it assesses the long-term glycemic status of the individual for the previous 90–120 days. HbA1c levels in blood are stable and do not fluctuate when compared to the random blood glucose levels. The normal level of HbA1c is 4–6.0%, while concentrations > 6.5% denote diabetes. Conventionally, HbA1c is measured using techniques such as chromatography, spectroscopy, immunoassays, capillary electrophoresis, fluorometry, etc., that are time-consuming, expensive, and involve complex procedures and skilled personnel. These limitations have spurred development of sensors incorporating nanostructured materials that can aid in specific and accurate quantification of HbA1c. Various chemical and biological sensing elements with and without nanoparticle interfaces have been explored for HbA1c detection. Attempts are underway to improve the detection speed, increase accuracy, and reduce sample volumes and detection costs through different combinations of nanomaterials, interfaces, capture elements, and measurement techniques. This review elaborates on the recent advances in the realm of electrochemical detection for HbA1c detection. It also discusses the emerging trends and challenges in the fabrication of effective, accurate, and cost-effective point-of-care (PoC) devices for HbA1c and the potential way forward.

Human procalcitonin (PCT) is a peptide precursor of the calcium-regulating hormone calcitonin. Traditionally, PCT has been used as a biomarker for severe bacterial infections and sepsis. It has also been recently identified as a potential marker for COVID-19. Normally, serum PCT is intracellularly cleaved to calcitonin, which lowers the levels of PCT (<0.01 ng/mL). In severe infectious diseases and sepsis, serum PCT levels increase above 100 ng/mL in response to pro-inflammatory stimulation. Development of sensors for specific quantification of PCT has resulted in considerable improvement in the sensitivity, linear range and rapid response. Among the various sensing strategies, electrochemical platforms have been extensively investigated owing to their cost-effectiveness, ease of fabrication and portability. Sandwich-type electrochemical immunoassays based on the specific antigen–antibody interactions with an electrochemical transducer and use of nanointerfaces has augmented the electrochemical response of the sensors towards PCT. Identification of a superior combination of electrode material and nanointerface, and translation of the sensing platform into flexible and disposable substrates are under active investigation towards development of a point-of-care device for PCT detection. This review provides an overview of the existing detection strategies and limitations of PCT electrochemical immunosensors, and the emerging directions to address these lacunae.

A facile one-pot synthesis of mono(hpp)- or di(hpp)-substituted N-heterocyclic ligands from halogenated N-heterocycles and 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (H-hpp) is presented. N,N-Bidentate and N,N,N-tridentate ligands incorporating electron-donating and electron-withdrawing substituents can also be readily synthesized using this method.

A tripodal squaramide–quinoline– tris(2-aminoethyl)amine (TREN) chemosensor, TSQAQ, was synthesised in good yield using diethylsquarate, 8-aminoquinoline and tris(2aminoethyl)amine as starting materials. The chemosensor was evaluated as a dual-mode colorimetric platform for the selective naked-eye detection of Cu2+ in DMSO and Cd2+ (precursor was cadmium acetate, CA) in acetonitrile. TSQAQ exhibited sensitivity towards Cu2+ via the ligand-to-metal charge transfer (LMCT) mechanism, producing an absorption peak at 450 nm and a distinctive colour change from colourless to bright yellow, irrespective of the Cu2+ counteranion screened. In contrast, the addition of CA yields an absorption peak at 420 nm and a colour transformation from colourless to pale yellow, with confirms the cooperative binding of Cd2+ by the squaramide moiety through hydrogen bonding. The limits of detection (LODs) were determined to be 97 nM (Cu2+) and 3 nM (Cd2+). Binding constants of 2.51 × 104 M-1 and 1.97 × 104 M-1 were determined using the Benesi-Hildebrand equation. The binding stoichiometry of TSQAQ with Cd2+ was established as 1:1 using the Job plot method. FTIR and 1H NMR titration studies indicated the involvement of TREN nitrogen, quinoline imine nitrogen, and squaramide carbonyl oxygen atoms in metal-ion coordination. Cu2+ sensing was reversible upon the addition of EDTA, with 94% signal recovery maintained over five cycles, enabling the implementation of an INHIBIT molecular logic gate. For practical applications, TSQAQ-coated paper strips were employed for the naked-eye detection of Cu2+ ions in real environmental water samples, including river water, seawater, and tap water.