3D-printed molecule-recognized photoelectrochemical sensing platform by expansion-flow-induced vertical alignment of graphene nanosheets for urea assay.

Channel-aligned modulation of a molecule-recognized photoelectrode to generate superior light-absorbing yet high-level analyte-adsorbing is pivotal but challenging for implementing highly sensitive and selective photoelectrochemical sensing. Herein, we demonstrated an innovative expansion-flow-modulated direct ink writing (DIW) 3D printing coupled with molecular imprinting technology for controllably building a microlattice-shaped photoelectrochemical sensor, with multiscale well-interconnected aligned channels created by vertically aligned arrangement of molecule-recognized photoactive graphene (G) nanosheets within printed filaments and regularly orthogonal layer-by-layer assembly of filaments. The unique architectural merit enabled rapid analyte diffusion and ready light spreading to photoactive and specific recognition sites located at all channel walls, thus endowing the sensor with a combined feature of prominent light absorption and analyte trapping. As a result, the 3D-printed (3DP) vertically aligned photoelectrochemical sensor with specific recognition sites displayed its remarkable capability for urea assay, with rapid response, low detection limit (10 nM), wide linear range (0.03-1100 µM), excellent selectivity, and working stability. This work has shed light on new strategies for processing advanced photoelectrochemical sensing architectures toward highly sensitive and selective assay.