(368y) A Paper-Based Point-of-Care Device for the Detection of Cysteine Using Gold Nanoparticles from Whole Blood

ABSTRACT

Cysteine (Cys), a sulfur-containing aminothiol, is vital for numerous metabolic functions and acts as a key biomarker for various health conditions. Low levels of Cys are associated with skin lesions, liver damage, hair depigmentation, fat loss, and reduced antioxidant defenses, whereas high levels are linked to cardiovascular and neurotoxic diseases. Precise measurement of Cys is important in both the food and pharmaceutical industries. Traditional methods such as high-performance liquid chromatography (HPLC), mass spectrometry, and electrochemical techniques are sensitive and reliable but are also complex and costly, which limits their practical application in point-of-care (POC) settings. Recent advancements in colorimetric sensing using noble metal nanoparticles (NPs) provide a promising solution for the rapid and specific detection of Cys. A microfluidic paper-based analytical device (μPADs) is gaining attention due to its cost-effectiveness, ease of fabrication, and suitability for various applications, including medical diagnostics. Despite these advancements, there is a need for μPADs that can operate under dry conditions to enhance storage and commercial viability. While freshly prepared NPs exhibit stability, they are prone to aggregation and environmental sensitivity during long-term dry storage. Thus, developing a simple and effective method for the stable, long-term storage of dried NPs is essential for their practical application. We present a colorimetric probe based on polyvinylpyrrolidone-capped gold nanoparticles (PVP–AuNPs) that is sensitive and selective for Cys. A μ-PAD with embedded dried PVP–AuNPs at the polyethersulfone (PES) paper surface is used for Cys detection (shown in Fig. 1). When thiol molecules attach to PVP–AuNPs in the presence of Cys, they clump together, and this causes the solution's color to shift from red to blue within 5 min. The device is capable of detecting Cys levels between 1.0 μM and 50.0 μM with a limit of detection (LOD) of 0.2 μM under optimized conditions. The stability of the μ-PAD was tested for 100 days, demonstrating re-dispersibility to detect Cys levels in blood. Dried PVP–AuNP–μPADs were integrated with blood plasma separation modules for POC Cys detection. Consequently, the device shows potential as a self-sustaining, quantification platform with a recovery percentage ranging from 98.44 to 111.9 in clinical samples.

Keywords: Cysteine (Cys), Microfluidic paper-based analytical device (μPADs), Gold nanoparticles (AuNPs), point-of-care (POC)

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