On the origin of photoluminescence of noble metal NCs, there are always hot debates: metal-centered quantum-size confinement effect VS ligand-centered surface state mechanism. Herein, we provided solid evidence that structural water molecules (SWs) confined in the nanocavity formed by surface-protective-ligand packing on the metal NCs are the real luminescent emitters of Au-Ag bimetal NCs. The Ag cation mediated Au-Ag bimetal NCs exhibit the unique pH-dependent dual-emission characteristic with larger Stokes shift up to 200 nm, which could be used as potential ratiometric nanosensors for pH detection. Our results provide a completely new insight on the understanding of the origin of photoluminescence of metal NCs, which elucidates the abnormal PL emission phenomena, including solvent effect, pH-dependent behavior, surface ligand effect, multiple emitter centers, and large-Stoke’s shift.

Surface states-the electronic states arising as a result of the different bonding environment-are easily contaminated by adsorbed molecules at nanoscale interfaces of metal nanoparticles (NPs), which generally poison the active sites of heterogeneous catalysts. Herein, we use selective hydrogenation of cinnamaldehyde (CAL) on platinum-covered titanium oxide (Pt@P25) as a prototype reaction, and show that the competitive exchange of extra-introduced species (sodium hydroxide and sodium formate) with spontaneously formed weak bound carbonate and bicarbonate anions at Pt NPs can reconstruct the surface states, which directs the preferred adsorption of the conjugated C=O and C=C double bonds of CAL, and consequently, results in highly efficient synthesis of unsaturated alcohol cinnamyl alcohol (COL) and saturated aldehyde hydrocinnamaldehyde (HCAL) with high selectivity of 94.7% and 97.6%, respectively. Our concept of restructured surface states to tune the chemoselectivity of α, β-unsaturated aldehydes triggered by the selective adsorption of alien molecules may lead to new design principles of heterogeneous catalysts, beyond the conventional d-band theory.

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Dual-mode bioanalysis integrating photoelectrochemical (PEC) and other modes is emerging and allows signal cross-checking for more reliable results. Metal–organic frameworks (MOFs) have been shown to be attractive materials in various biological applications. This work presents the utilization of MOF encapsulation and stimuli-responsive decapsulation for dual-mode PEC and fluorescence (FL) bioanalysis. Photoactive dye methylene violet (MV) was encapsulated in zeolitic imidazolate framework-90 (ZIF-90) to form an MV@ZIF-90 hybrid material, and MV could be released by adenosine triphosphate (ATP)-induced ZIF-90 disintegration. The released MV not only had FL emission but also had a sensitization effect on the ZnIn2S4 (ZnInS) photoanode. Based on the MV-dependent sensitization effect and FL emission characteristic, a dual-mode PEC–FL strategy was established for ATP detection with low detection limits, that is, 3.2 and 4.1 pM for PEC and FL detection, respectively. This study features and will inspire the construction and implementation of smart MOF materials for dual-mode bioanalysis.

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