Detection of hydrogen peroxide using hemin-PEI/MWCNT-modified screen-printed graphene electrodes: Toward feasibility in exhaled breath condensate

Abstract

Detection of H<inf>2</inf>O<inf>2</inf> in exhaled breath condensate is a simple, safe, and non-invasive approach for assessing oxidative stress, inflammation in the respiratory tract, or respiratory diseases. However, this breath biopsy approach lacks sensitive and stable detection tools. Here, we report a robust electrochemical sensor based on an “artificial peroxidase” hemin-polyethyleneimine complex, assembled onto multi-walled carbon nanotube-modified screen-printed graphene electrodes by a facile drop-casting approach. The sensor enables efficient electrocatalytic reduction of H<inf>2</inf>O<inf>2</inf>, starting from –0.1 V vs. Ag/AgCl, with an electron transfer (ET) rate of 2.41 s⁻¹. The sensor’s performance was first evaluated using standard H<inf>2</inf>O<inf>2</inf> in a 20 mM phosphate buffer solution containing 0.15 M NaCl (pH 7.0). Amperometric detection of H<inf>2</inf>O<inf>2</inf> at –0.2 V showed two linear ranges, at 1–10 µM and 30–1000 µM H<inf>2</inf>O<inf>2</inf>, with a limit of detection determined as 0.11 µM H<inf>2</inf>O<inf>2</inf> (3SD<inf>blank</inf>/slope). The corresponding sensitivities were 18.09 ± 0.89 and 0.18 ± 1.02 A M⁻¹ cm⁻², respectively. The sensor showed high selectivity toward H<inf>2</inf>O<inf>2</inf>, with less than ±5 % signal deviation in the presence of common interferents, and retained stable performance for up to 30 days under refrigerated storage in a sealed zip-lock bag. Applied to real exhaled breath condensate samples, the sensor enabled detection down to 0.13 µM, with acceptable recoveries of 80.96 %–106.73 % and RSDs of 4.24 %–10.03 %. Our results demonstrate a simple and sustainable approach for the sensitive detection of H<inf>2</inf>O<inf>2</inf> in exhaled breath condensate, offering proof-of-concept for non-invasive monitoring of oxidative stress.