A new application of papain: As a peroxidase-like catalyst for fluorometric detection of uric acid

Uric acid detection via dual-mode mechanism with copper-coordinated nitrogen-doped carbon dots as peroxidase mimics

Monitoring disease-related biomarkers, such as uric acid in human body fluids, is essential for effective disease management and clinical diagnosis. In this study, copper-coordinated nitrogen-doped carbon dots (Cu@N-CDs) were synthesized via a simple hydrothermal method, achieving a remarkable photoluminescence quantum yield of 44.69%. The Cu@N-CDs emitted fluorescence at 460 nm upon excitation at 360 nm, making them highly suitable for sensitive biosensing applications. For uric acid detection, a Cu@N-CDs-based probe was developed and coupled with phenol (ph-OH) and 4-aminoantipyrine (AP-NH2). In the presence of hydrogen peroxide (H2O2), generated through the enzymatic breakdown of uric acid by uricase, ph-OH and AP-NH2 reacted to form a pink-colored compound. This compound quenched the fluorescence emission of Cu@N-CDs via an inner-filter effect, enabling fluorometric detection. Additionally, for colorimetric detection, the pink compound was quantified by measuring absorbance at 510 nm. The detection strategy utilized the peroxidase-mimetic activity of Cu@N-CDs, which was further enhanced by the presence of Cu. Under optimized conditions, the fluorometric method demonstrated a linear detection range of 0.01-700 μM, while the colorimetric method showed a range of 0.07-700 μM for uric acid. The developed approach proved highly effective in detecting uric acid in human blood serum and urine samples, yielding accurate results with acceptable recovery rates. This dual-mode detection method offers a reliable, sensitive, and cost-effective tool for monitoring uric acid levels, marking a significant advancement in clinical diagnostics and personalized healthcare.

Non-enzymatic Detection of Uric Acid in Serum and Urine by Fluorescent and Visual Dual-Mode Sensor Based on 3-aminophenylboric Acid Functionalized Carbon Dots

Herein, we developed a sophisticated dual-mode sensor that utilized 3-aminophenylboric acid functionalized carbon dots (APBA-CDs) to accurately detect uric acid (UA). Our innovative process involved synthesizing APBA-CDs that emitted at 369 nm using a one-step hydrothermal method with 3-aminophenylboric acid and L-glutamine as precursors, ethanol and deionized water as solvents. Once UA was introduced to the APBA-CDs, the fluorescence of the system became visibly quenched. The results of Zeta potential, Fourier transformed infrared (FTIR) spectra, fluorescence lifetime, and other characteristics were analyzed to determine that the reaction mechanism was static quenching. This meant that after UA was mixed with APBA-CDs, it combined with the boric acid function on the surface to form complexes, resulting in a decrease in fluorescence intensity and a blue shift in the absorption peak at about 295 nm in the Ultraviolet-visible (UV-vis) absorption spectra. We were pleased to report that we have successfully used the dual-reading platform to accurately detect UA in serum and human urine. It provided a superior quantitative and visual analysis of UA without the involvement of enzymes. We firmly believe that our innovative dual-mode sensor has immense potential in the fields of biosensing and health monitoring.

Plant and Arthropod IgE-Binding Papain-like Cysteine Proteases: Multiple Contributions to Allergenicity

Papain-like cysteine proteases are widespread and can be detected in all domains of life. They share structural and enzymatic properties with the group's namesake member, papain. They show a broad range of protein substrates and are involved in several biological processes. These proteases are widely exploited for food, pharmaceutical, chemical and cosmetic biotechnological applications. However, some of them are known to cause allergic reactions. In this context, the objective of this review is to report an overview of some general properties of papain-like cysteine proteases and to highlight their contributions to allergy reactions observed in humans. For instance, the literature shows that their proteolytic activity can cause an increase in tissue permeability, which favours the crossing of allergens through the skin, intestinal and respiratory barriers. The observation that allergy to PLCPs is mostly detected for inhaled proteins is in line with the reports describing mite homologs, such as Der p 1 and Der f 1, as major allergens showing a frequent correlation between sensitisation and clinical allergic reactions. In contrast, the plant food homologs are often digested in the gastrointestinal tract. Therefore, they only rarely can cause allergic reactions in humans. Accordingly, they are reported mainly as a cause of occupational diseases.