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The development of immobilization method of a chemoprobe on solid support without sacrificing its good original performance in homogeneous solution is a tricky problem. Herein, we make use of the transparent agarose hydrogel with semi-wet property which provided appropriate microenvironment to immobilize the chemoprobe and maintained its original performance to develop an excellent smartphone-enabled colorimetric platform. As a proof of concept, the sensing platform was fabricated with agarose hydrogel that captured diethylaminoethyldextran chloride (DEAE-dextran) and dithiothreitol modified copper nanoclusters (Cu NCs) as a fluorescence probe. Benefiting from the aggregation-induced emission (AIE) effect and confinement effect of hydrogel, the fluorescence quantum yield (QY) of Cu NCs hydrogel is three times higher than that of Cu NCs. Moreover, sensitively detection of Cr(VI) can be realized in the concentration range of 0.07–38.00 μM based on the amplified fluorescence probe. The outstanding analysis performance for Cr(VI) is also achieved when Cu NCs hydrogel was directly immobilized on paper as a smartphone-enabled colorimetric platform, indicating that our strategy can promote the further development of the application of hydrogel materials. [Display omitted] • An AIE-active copper nanoclusters (Cu NCs) functionalized hydrogel was prepared. • The amplified fluorescent detection of Cr(VI) by Cu NCs hydrogel was achieved. • Cu NCs hydrogel as a smartphone-enabled colorimetric platform showed an outstanding performance of detecting Cr(VI). • Smartphone-enabled colorimetric platform can realize instrument-free, portable and on-site detection of Cr(VI). [ABSTRACT FROM AUTHOR]