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Treatment of cryptococcal meningitis relies primarily on flucytosine (5FC), which is also used to treat candidiasis and infections caused by Cryptococcus neoformans. High dosages of this drug, despite its therapeutic properties, may cause hazardous side effects such as bone marrow suppression, hepatotoxicity, and gastrointestinal toxicity. The detection of trace amounts of 5FC medication may aid in tracking the treatment's efficacy and mitigating unwanted effects. Surface-enhanced Raman spectroscopy (SERS) is a rapid, reliable, and precise approach for detecting extremely low amounts of biological and chemical compounds. A filter paper-based SERS biosensor coated with silver nanoparticles (AgNPs) were employed to detect the 5FC drug. The AgNPs fabricated via the chemical reduction method were characterized by FE-SEM, TEM, XRD, AFM, and UV-Vis spectroscopy. Plasmonic active sites were made by coating the filter paper substrate with AgNPs to detect the 5FC drug's molecular vibrations. As the 5FC drug was coated onto the filter paper substrate, the AgNPs interacted with it, allowing for the detection of very low concentrations of the drug. The SERS filter paper substrate could detect concentrations of 5FC as low as 10−10 M. The Raman spectra and peak signals obtained experimentally were also simulated and validated using the density functional theory (DFT) approach. Six sets of measurements were taken, and the average RSD was obtained to be 4.62%. The experimentally measured enhancement factor for recognizing molecular vibrations of the 5FC was 9.065 × 107, and it was numerically estimated as 10.044 × 107. Therefore, the fabricated SERS-based filter paper substrate is useful for drug monitoring since they can detect even trace amounts of the targeted drug. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface-enhanced Raman scattering (SERS) method was used to detect the antiviral drug Acyclovir. • SERS-active plasmonic substrates were prepared using filter paper substrates decorated with silver nanoparticles. • Developed SERS-active substrates indicated favorable reproducibility and chemical stability, with a limit of detection (LOD) of 10-12 M. • FDTD simulations were carried out, and the electric field distributions as well as the enhancement factor of the developed SERS-active substrates were obtained. Acyclovir (ACV) drug, a common antiviral agent, is frequently used as the primary clinical treatment method for treating hepatitis B, herpes simplex, and varicella zoster viruses due to its potent therapeutic effect. In patients with compromised immune systems, this medication can stop cytomegalovirus infections, and high doses of this drug are required; however, such prescription leads to kidney toxicity. Therefore, timely and accurate detection of ACV is crucial in many areas. Surface-Enhanced Raman Scattering (SERS) is a reliable, rapid, and precise approach for the identification of trace biomaterials and chemicals. Filter paper substrates decorated with silver nanoparticles (AgNPs) were applied as SERS biosensors to detect ACV and control its adverse effects. Initially, a chemical reduction procedure was utilized to produce AgNPs. Afterward, UV–Vis, FE-SEM, XRD, TEM, DLS, and AFM were employed to examine the properties of prepared AgNPs. In order to prepare SERS-active filter paper substrates (SERS-FPS) to detect Molecular vibrations of ACV, AgNPs prepared by immersion method were coated on filter paper substrates. Moreover, the UV–Vis DRS analysis was carried out to assess the stability of filter paper substrates and SERS-FPS. The AgNPs reacted with ACV after being coated on SERS-active plasmonic substrates and could sensitively detect ACV in small concentrations. It was discovered that the limit of detection of SERS plasmonic substrates was 10-12 M. Moreover, the mean RSD for ten repeated tests was calculated as 4.19%. The enhancement factor for detecting ACV using the developed biosensors was calculated to be 3.024 × 105 and 3.058 × 105 experimentally and via simulation, respectively. According to the Raman results, SERS-FPS for the detection of ACV, fabricated by the present methods, showed promising results for SERS-based investigations. Furthermore, these substrates showed significant disposablity, reproducibility, and chemical stability. Therefore, the fabricated substrates are capable to be employed as potential SERS biosensors to detect trace substances. [ABSTRACT FROM AUTHOR]