A shortened 8-mer ssDNA aptamer was successfully truncated for four different tetracyclines with high affinity. The ultrasensitive colorimetric detection of oxytetracycline using this shortened aptamer was possible, which was about 500-fold enhanced compared to that obtained using the original 76-mer aptamer.

A cognate aptamer duo for visceral adipose tissue-derived serpin (vaspin) which distinctively bind to two different sites on vaspin with high affinity and specificity were successfully developed by using graphene oxide-based systematic evolution of ligands by exponential enrichment (GO-SELEX), which offers immobilization-free screening of aptamers. The specific and simultaneous bindings of this aptamer duo (V1 and V49 aptamers) to the different sites of vaspin were confirmed by circular dichroism (CD) analysis and both sandwich-type surface plasmon resonance (SPR) and quantum dot labelled fluorescence imaging analysis (V1 aptamer serves as primary capturing aptamer and V49 aptamer as secondary signalling aptamer or vice versa). With this vaspin cognate aptamer duo on SPR platform, the detection of the target vaspin were improved to the limit of detection down to 3.5 ng/ml in buffer and 4.7 ng/ml in human serum samples. This cognate aptamer duo based biosensor could be utilized in the early diagnosis of type-2 diabetes.

A rapid and sensitive sandwich electrochemical immunosensor was developed based on the fabrication of the graphene/polyaniline (GP/PANI) nanocomposite onto screen-printed gold electrode (SPGE) for detection of tuberculosis biomarker 10-kDa culture filtrate protein (CFP10). The prepared GP/PANI nanocomposite was characterized using Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM). The chemical bonding and morphology of GP/PANI-modified SPGE were studied by Raman spectroscopy and FESEM coupled with energy dispersive X-ray spectroscopy, respectively. From both studies, it clearly showed that GP/PANI was successfully coated onto SPGE through drop cast technique. Cyclic voltammetry was used to study the electrochemical properties of the modified electrode. The effective surface area for GP/PANI-modified SPGE was enhanced about five times compared with bare SPGE. Differential pulse voltammetry was used to detect the CFP10 antigen. The GP/PANI-modified SPGE that was fortified with sandwich type immunosensor exhibited a wide linear range (20–100 ng/mL) with a low detection limit of 15 ng/mL. This proposed electrochemical immunosensor is sensitive, low sample volume, rapid and disposable, which is suitable for tuberculosis detection in real samples.

A portable electrochemical aptamer-antibody based sandwich biosensor has been designed and successfully developed using an aptamer bioreceptor immobilized onto a screen-printed electrode surface for Mycobacterium tuberculosis (M. tuberculosis) detection in clinical sputum samples. In the sensing strategy, a CFP10-ESAT6 binding aptamer was immobilized onto a graphene/polyaniline (GP/PANI)-modified gold working electrode by covalent binding via glutaraldehyde linkage. Upon interaction with the CFP10-ESAT6 antigen target, the aptamer will capture the target where the nano-labelled Fe₃O₄/Au MNPs conjugated antibody is used to complete the sandwich format and enhance the signal produced from the aptamer–antigen interaction. Using this strategy, the detection of CFP10-ESAT6 antigen was conducted in the concentration range of 5 to 500 ng/mL. From the analysis, the detection limit was found to be 1.5 ng/mL, thereby demonstrating the efficiency of the aptamer as a bioreceptor. The specificity study was carried out using bovine serum albumin (BSA), MPT64, and human serum, and the result demonstrated good specificity that is 7% higher than the antibody–antigen interaction reported in a previous study. The fabricated aptasensor for M. tuberculosis analysis shows good reproducibility with an relative standard deviation (RSD) of 2.5%. Further analysis of M. tuberculosis in sputum samples have shown good correlation with the culture method with 100% specificity and sensitivity, thus making the aptasensor a promising candidate for M. tuberculosis detection considering its high specificity and sensitivity with clinical samples.