Paper based modification-free photoelectrochemical sensing platform with single-crystalline aloe like TiO as electron transporting material for cTnI detection.

By controlling target-induced signal quencher release, a label-free and modification-free microfluidic paper based photoelectrochemical analytical device (μ-PAD) for cardiac troponin-I (cTnI) detection was designed for the first time. To achieve it, cellulose paper based single-crystalline three-dimensional aloe like TiO arrays (PSATs) were firstly fabricated as the electron transporting material, providing direct pathways for the charge carriers transfer, and subsequently coupled with CdS to form PSATs/CdS heterojunction for extending the solar spectrum response. Meanwhile, positive charged mesoporous silica nanoparticles (PMSNs) were prepared as the nanocarrier to efficient entrap the Cu which could be regarded as signal quencher due to their reaction with CdS to form CuS. Single stranded DNAs (ssDNAs), which could bind specifically with the target of cTnI, were then introduced to couple with the PMSNs and used as the bio-gate to encapsulate the signal quencher of Cu, endowing the functional PMSNs with responsiveness to cTnI. When the cTnI existed, the ssDNAs were dissociated from PMSNs due to the formation of cTnI-ssDNAs complexes, triggering controllable release of the trapped Cu, and further decreasing the photocurrent signal caused by the formation of CuS. Accordingly, the concentration of cTnI could be accurately quantified via the photocurrent, realizing the target-induced modification-free μ-PAD assay. We believe this work could provide an ingenious idea to construct the easy-to-use novel modification-free μ-PAD.