biostudies-literatureKim YMinistry of Science ICT and Future PlanningKorea University Grant and the BK21 FOURNational Research Foundation of Korea4081https://www.ebi.ac.uk/biostudies/studies/S-EPMC9699376biostudies-literatureUnknown12(22)Hydrogels containing redox-sensitive colorimetric nanoparticles (NPs) have been used to sense ambient pH in many fields owing to their simple and fast visualization capabilities. However, real-time pH monitoring still has limitations due to its poor response rate and irreversibility. Herein, we developed a fast responsive colorimetric hydrogel called ferrocene adsorption colorimetric hydrogel (FACH). Ferrocene, an organometallic compound, plays a vital role as an electron transfer mediator (i.e., redox catalyst) within the hydrogel network. FACH shows fast color change performance with high reactivity and penetrability to ambient pH changes. In detail, FACH shows distinct color change within 2 min under various pH conditions from four to eight, with good reliability. The speed for color chNanomaterials (Basel, Switzerland)Fast Responsive, Reversible Colorimetric Nanoparticle-Hydrogel Complexes for pH Monitoring.PMC9699376NRF-2021R1C1C1012822KMDF_PR_20200901_0127NRF-2022R1I1A1A01072687NRF-2021R1A4A1028969NRF-2020R1A2C2102262Korea University Grant and the BK21 FOURPark IHu JHong YLee KKim YPark SLee GLee TKim MfalseFast Responsive, Reversible Colorimetric Nanoparticle-Hydrogel Complexes for pH Monitoring.Hydrogels containing redox-sensitive colorimetric nanoparticles (NPs) have been used to sense ambient pH in many fields owing to their simple and fast visualization capabilities. However, real-time pH monitoring still has limitations due to its poor response rate and irreversibility. Herein, we developed a fast responsive colorimetric hydrogel called ferrocene adsorption colorimetric hydrogel (FACH). Ferrocene, an organometallic compound, plays a vital role as an electron transfer mediator (i.e., redox catalyst) within the hydrogel network. FACH shows fast color change performance with high reactivity and penetrability to ambient pH changes. In detail, FACH shows distinct color change within 2 min under various pH conditions from four to eight, with good reliability. The speed for color ch2022-01-01T00:00:00Z2022 Nov2025-04-26T05:21:44.226Z2025-04-06T11:27:29.953ZS-EPMC96993763643236610.3390/nano12224081