# Nitrogen-Doped Biochar Derived from Starch for Enzyme-Free Colorimetric Detection of Uric Acid in Human Body Fluids

## TL;DR

A new method uses nitrogen-doped biochar to detect uric acid in body fluids without enzymes, offering high sensitivity and accuracy.

## Contribution

A novel enzyme-free colorimetric platform using nitrogen-doped biochar for uric acid detection is developed.

## Key findings

- The method detects uric acid with a detection limit of 4.87 μmol·L−1 and a wide linear range.
- The platform shows high selectivity, stability, and reproducibility in human body fluid samples.
- Spike-recovery rates in real samples ranged from 95.5% to 103.6%, indicating practical applicability.

## Abstract

Uric acid (UA), a key end-product of human purine metabolism, serves as an important biomarker linked to multiple disorders. This study developed a novel enzyme-free colorimetric sensing platform based on starch-derived nitrogen-doped biochar (NC) for the highly sensitive and selective detection of UA in human body fluids. The NC material with a high specific surface area and abundant nitrogen active sites was prepared via a two-step strategy involving hydrothermal synthesis followed by high-temperature pyrolysis, using starch and urea as raw materials. Under mild conditions, the NC effectively catalyzes dissolved oxygen to produce reactive oxygen species (·O2− and 1O2), which oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue-colored oxidation product (TMBox). The presence of UA reduces TMBox to colorless TMB, leading to a measurable decrease in absorbance at 652 nm and enabling quantitative UA detection. Key reaction conditions were systematically optimized. Material characterization and mechanistic investigations confirmed the catalytic performance of the NC. The method demonstrated a wide linear response from 10 to 500 μmol·L−1, with a detection limit of 4.87 μmol·L−1, and demonstrated outstanding selectivity, stability, and reproducibility. Practical application in human serum and urine samples yielded results consistent with clinical reference ranges, and spike-recovery rates ranged from 95.5% to 103.6%, indicating great potential for real-sample analysis.