biostudies-literatureLu QCarl-Zeiss-StiftungBundesministerium f?r Bildung und ForschungDeutsche ForschungsgemeinschaftEuropean Research CouncilNatural Science Foundation of Guangdong ProvinceNational Natural Science Foundation of ChinaEuropean Commission7222-7232https://www.ebi.ac.uk/biostudies/studies/S-EPMC10958502biostudies-literatureUnknown146(11)Defect centers in a nanodiamond (ND) allow the detection of tiny magnetic fields in their direct surroundings, rendering them as an emerging tool for nanoscale sensing applications. Eumelanin, an abundant pigment, plays an important role in biology and material science. Here, for the first time, we evaluate the comproportionation reaction in eumelanin by detecting and quantifying semiquinone radicals through the nitrogen-vacancy color center. A thin layer of eumelanin is polymerized on the surface of nanodiamonds (NDs), and depending on the environmental conditions, such as the local pH value, near-infrared, and ultraviolet light irradiation, the radicals form and react in situ. By combining experiments and theoretical simulations, we quantify the local number and kinetics of free radicalsJournal of the American Chemical SocietyUnraveling Eumelanin Radical Formation by Nanodiamond Optical Relaxometry in a Living Cell.PMC109585022021A1515012030CRC 127903ZU1110FF499424854Ultrasens-Vir85643212074131316249678 - SFB 1279387073854Balasubramanian PPlenio MBSow MVolkert CJelezko FWeil TLieberwirth IGonzalez Brouwer RWang ZLu QGraf RWu YVosberg BfalseUnraveling Eumelanin Radical Formation by Nanodiamond Optical Relaxometry in a Living Cell.Defect centers in a nanodiamond (ND) allow the detection of tiny magnetic fields in their direct surroundings, rendering them as an emerging tool for nanoscale sensing applications. Eumelanin, an abundant pigment, plays an important role in biology and material science. Here, for the first time, we evaluate the comproportionation reaction in eumelanin by detecting and quantifying semiquinone radicals through the nitrogen-vacancy color center. A thin layer of eumelanin is polymerized on the surface of nanodiamonds (NDs), and depending on the environmental conditions, such as the local pH value, near-infrared, and ultraviolet light irradiation, the radicals form and react in situ. By combining experiments and theoretical simulations, we quantify the local number and kinetics of free radicals2024-01-01T00:00:00Z2024 Mar2025-04-22T13:04:40.755Z2025-04-06T00:29:21.43ZS-EPMC109585023846985310.1021/jacs.3c07720