Arzum Erdem

The discovery of clustered regularly ınterspaced short palindromic repeats (CRISPR)–CRISPR-associated protein (Cas) systems as potent molecular instruments has transformed biosensing for the detection of viruses. These programmable nucleases, originally derived from bacterial immune mechanisms, offer high specificity, sensitivity and adaptability, making them ideal for diagnosing a wide range of viral infections. CRISPR-based diagnostics, including DNA endonuclease-targeted CRISPR trans reporter (DETECTR) and specific high-sensitivity enzymatic reporter unlocking (SHERLOCK), have been developed for rapid, cost-effective and field-deployable detection of both DNA and RNA viruses. This chapter provides a comprehensive overview of CRISPR–Cas biosensing technologies, categorizing detection methods for viral families such as Coronaviridae, Flaviviridae, Retroviridae and others. It explores key detection platforms, including fluorescence, electrochemical and colorimetric biosensors, highlighting their integration with isothermal amplification techniques and nanomaterials to enhance detection performance. Additionally, the chapter discusses recent advancements, challenges in clinical translation and potential future directions, including regulatory considerations and the integration of CRISPR with artificial intelligence and microfluidics. These innovations position CRISPR–Cas biosensors as transformative tools for molecular diagnostics, offering unprecedented speed and precision in viral detection, with implications for outbreak management, global health security and personalized medicine.

A combination of chitosan (CHIT), gold composite, and ionic liquid (IL) modification was employed to construct novel pencil graphite electrodes (PGE) for the electrochemical investigation of curcumin-nucleic acid interaction. The electrochemical behaviour of these CHIT-Au-IL modified electrodes (CHIT-Au-IL-PGEs) was evaluated using techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Additionally, scanning electron microscopy (SEM) was utilized to analyse the surface morphology and structural features of the electrodes. Optimization studies on the interaction between curcumin and nucleic acids were conducted using electrochemical techniques. DNA concentration and immobilization time on the CHIT-Au-IL-PGE surface were optimized using cyclic voltammetry (CV), while curcumin concentration was investigated through differential pulse voltammetry (DPV). The detection limit for curcumin was determined to be 0.29 µg/mL (0.78 µM). The curcumin-DNA interaction was further analysed at varying time intervals using EIS. The proposed electrochemical method is efficient, user-friendly, and rapid, providing a promising tool for screening small molecule interactions with DNA.

An aptamer-based electrochemical biosensor was developed for the highly sensitive detection of SARS-CoV-2 S1 protein using electrodes modified with a multi-walled carbon nanotube–ionic liquid (MWCNT–IL) composite. Comprehensive electrochemical and microscopic characterizations of the MWCNT–IL material were conducted, followed by the optimization of experimental parameters including ionic liquid concentration and surface modification time. Critical parameters for aptasensor construction, aptamer concentration, immobilization time, and aptamer-protein interaction time, were also optimized. Under optimal conditions, the biosensor exhibited a wide linear response from 1 fg/mL to 1 ng/mL in buffer, with a remarkably low limit of detection (LOD) of 0.11 fg/mL. Selectivity evaluations against hemagglutinin antigen (HA) and MERS-CoV-S1 (MERS) protein confirmed the sensor’s high specificity for SARS-CoV-2 S1 protein. The sensor’s applicability in artificial saliva was also successfully demonstrated, yielding accurate quantification and low detection limits (LOD: 0.16 fg/mL). Recovery studies in artificial saliva demonstrated satisfactory accuracy, with recoveries ranging from 108% to 120% and high reproducibility. Notably, the aptasensor maintained strong selectivity even in the presence of matrix interferents. Furthermore, the potential for point-of-care use was assessed via a smartphone-connected portable potentiostat. This handheld system enabled a linear detection range of 1 fg/mL to 1 ng/mL with a LOD of 0.83 fg/mL. Collectively, these results highlight the MWCNT–IL-based aptasensor as a robust, low-cost, and portable platform for rapid COVID-19 diagnostics, offering considerable promise for deployment in point-of-care and resource-constrained environments. AbstractSection Graphical Abstract

COVID-19, caused by SARS-CoV-2, has created unprecedented global health challenges, necessitating rapid and reliable diagnostic strategies. The spike (S) protein, particularly its S1 subunit, plays a critical role in viral entry, making it a prime biomarker for early detection. In this study, we present a disposable, low-cost, and portable electrochemical biosensor employing specifically optimized aptamers (Optimers) for SARS-CoV-2 S1 recognition. The sensing approach is based on aptamer–protein complex formation in solution, followed by immobilization onto pencil graphite electrodes (PGEs). The key parameters, including aptamer concentration, interaction time, redox probe concentration, and immobilization time, were systematically optimized by performing electrochemical measurement in redox probe solution containing ferri/ferrocyanide using differential pulse voltammetry (DPV) technique.Under optimized conditions, the biosensor achieved an ultralow detection limit of 18.80 ag/mL with a wide linear range (10⁻¹–10⁴ fg/mL) in buffer. Importantly, the sensor exhibited excellent selectivity against hemagglutinin antigen and MERS-CoV-S1 protein, while maintaining high performance in artificial saliva with a detection limit of 14.42 ag/mL. Furthermore, its integration with a smartphone-connected portable potentiostat underscores strong potential for point-of-care use. To our knowledge, this is the first voltammetric biosensor utilizing optimized aptamers (Optimers) specific to SARS-CoV-2 S1 on disposable PGEs, providing a robust and field-deployable platform for early COVID-19 diagnostics.

Lignin, the second most abundant biopolymer in nature after cellulose, has attracted attention for its compatibility with carbon-based materials. In this study, lignin-modified single-use pencil graphite electrodes (PGE/LG) were developed for the electrochemical detection of fish sperm DNA (fsDNA), the anticancer drug Mitomycin C (MC), and their interaction. The modified electrodes were characterized using field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques. Differential pulse voltammetry (DPV) in ferri/ferrocyanide redox probe solution was employed for signal monitoring. The detection limits were calculated as 2.95 ng/mL for fsDNA between 10¹ and 10⁵ ng/mL and 0.22 pg/mL for MC between 1 and 10⁶ pg/mL. Furthermore, the interaction of DNA with MC was evaluated by DPV and EIS techniques. The cross-linking between MC and the guanine bases of DNA inhibited electron transfer, resulting in a decrease in current response and an increase in charge transfer resistance. These results demonstrate the potential of the PGE/LG platform as a cost-effective, sensitive, and rapid biosensor for DNA detection, anticancer drug analysis, and drug–DNA interaction studies.