Electrochemically mediated atom transfer radical polymerization (eATRP) initiates/controls the controlled/living ATRP chain propagation process by electrochemically generating (regenerating) the activator (lower-oxidation-state metal complex) from deactivator (higher-oxidation-state metal complex). Despite successful demonstrations in both of the homogeneous polymerization and heterogeneous systems (namely, surface-initiated ATRP, SI-ATRP), the eATRP process itself has never been in situ investigated, and important information regarding this process remains unrevealed. In this work, we report the first investigation of the electrochemically mediated SI-ATRP (eSI-ATRP) by rationally combining the electrochemical technique with real-time surface plasmon resonance (SPR). In the experiment, the potential of a SPR gold chip modified by the self-assembled monolayer of the ATRP initiator was controlled to electrochemically reduce the deactivator to activator to initiate the SI-ATRP, and the whole process was simultaneously monitored by SPR with a high time resolution of 0.1 s. It is found that it is feasible to electrochemically trigger/control the SI-ATRP and the polymerization rate is correlated to the potential applied to the gold chip. This work reveals important kinetic information for eSI-ATRP and offers a powerful platform for in situ investigation of such complicated processes.

•Metallic cobalt nanoparticle decorated graphene aerogel was synthesized.•It demonstrates commercial Pt/C-comparable ORR activity.•Metallic cobalt is highly efficient to boost the ORR activity of neighboring carbon.Transition metals have attracted particular research interest for sustainable ORR electrocatalysis but zero-valent ones have been often ignored. In this work metallic cobalt nanoparticle decorated graphene aerogel (CoNPs/rGO aerogel) was synthesized via a facile hydrothermal reaction, followed by thermal annealing in reducing H2 atmosphere. As-prepared CoNPs/rGO aerogel demonstrates commercial Pt/C-comparable ORR activity through a predominant four-electron pathway, as well as excellent durability and methanol tolerance superior to Pt/C in alkaline medium. This work suggests that metallic cobalt nanoparticle is highly efficient to boost the ORR activity of neighboring carbon besides various cobalt compounds.

•Fe/Fe3C nanoparticles loaded on Fe/N-doped graphene was synthesized.•The catalyst demonstrates excellent activity and durability in Fenton reaction.Heterogeneous Fenton catalyst with high activity and excellent durability is highly demanded for efficient removal of organic pollutants via well-known Fenton reaction. In this work Fe/Fe3C nanoparticles loaded on iron/nitrogen-doped graphene (Fe/Fe3C@Fe/N-Graphene) were synthesized via spontaneous oxidative polymerization of dopamine (DA) on graphene oxide (GO) surface in the presence of iron (III) chloride, followed by thermal annealing. The Fenton catalytic performance of as-prepared Fe/Fe3C@Fe/N-Graphene was evaluated by degrading rhodamine 6G (Rh 6G) as a model organic pollutant. It is found that as-prepared catalyst demonstrates good activity with a rate constant of 0.080 min−1 under optimal hydrogen peroxide (H2O2) concentration and catalyst dosage. Moreover, its catalytic activity shows negligible decrease even after 13 successive cycles, exhibiting excellent catalytic durability. The possible mechanism behind the improved Fenton catalytic activity and durability was further discussed.Download high-res image (127KB)Download full-size image

•A novel label-free PEC immunosensor based on PDA-coated ZnO nanorods was reported.•PDA serves simultaneously as a sensitizer and a probe attachment matrix.•A detection limit of 10 pg mL−1 was achieved.•The dynamic range spans from 10 pg mL−1 to 500 ng mL−1.Photoelectrochemical (PEC) detection is a promising method for label-free immunoassay by reporting the specific biological recognition events with electrical signals. However, it is challenging to rationally incorporate immunosensing components with a photocurrent conversion interface, which generally necessitates multistep fabrication and careful tailoring of various components such as photoactive material and biological probe. For high detection reliability and reproducibility, it is highly desirable to rationally construct an efficient PEC interface with architecture as simple as possible. In this work, a novel yet simple PEC immunosensor based on bio-inspired polydopamine (PDA) thin film-coated zinc oxide (ZnO) nanorods was reported. In this PEC immunosensor, the PDA thin film serves simultaneously as a unique sensitizer for charge separation as well as a functional layer for probe antibody attachment. The photocurrent on this electrode under illumination decreases upon the immunoreaction on the surface, possibly due to the blocking effect of formed immunocomplexes on the access of reducing reagent to the photoelectrode, thus offering a simple and reliable platform for PEC label-free immunoassay. By using an antibody-antigen pair as a model, successful label-free immunoassay was achieved with a detection limit of 10 pg mL−1 and a dynamic range from 100 pg mL−1 to 500 ng mL−1. This work demonstrates intriguing electro-optical property and bioconjugation activity of PDA film and may pave the way toward advanced PEC immunoassays.In this work, a novel yet simple PEC immunosensor based on bio-inspired polydopamine (PDA) thin film-coated ZnO nanorods was reported. In this photoelectrochemical immunosensor, the PDA thin film serves simultaneously as a unique sensitizer for charge separation as well as a functional layer for probe antibody attachment. The photocurrent on this electrode under illumination decreases upon the immunoreaction on the surface, possibly due to the blocking effect of formed immunocomplexes on the access of reducing reagent to the photoelectrode, thus offering a simple and reliable platform for PEC label-free immunoassay. By using an antibody-antigen pair as a model, successful label-free immunoassay was achieved with a detection limit of 10 pg mL−1 and a dynamic range from 100 pg mL−1 to 500 ng mL−1. This work demonstrates intriguing electro-optical property and bioconjugation activity of PDA film and may pave the way toward advanced PEC immunoassays.

Heteroatom-doped graphene have encouraged intensive research as promising metal-free oxygen reduction reaction (ORR) electrocatalysts but the correlation between the precursor material and final ORR activity remains unclear. In this work a serial of nitrogen/sulfur (N/S)-doped graphene catalysts were synthesized by modifying graphene oxide (GO) with cysteine as a N/S source and sequential thermal annealing. It is disclosed that the cysteine-GO reaction time shows a significant influence on the ORR activity of N/S-doped graphene. A unique process of oxidation-induced in situ disulfide formation is further found to be involved in the synthesis of optimal N/S-doped graphene, which displays ORR activity superior to commercial Pt/C in alkaline media. This work suggests that the heteroatom source itself and careful optimization of reaction conditions are critical to obtain high performance doped-graphene electrocatalyst.Download high-res image (94KB)Download full-size image

Various approaches have been developed to visualize a latent fingerprint (LFP) for personal identification, but simultaneous transfer of a LFP for preservation has yet to be achieved. We herein report a novel strategy for simultaneous transfer and imaging of LFPs on a broad variety of substrates by using the interfacial separation of polydopamine (PDA) thin film, followed by electroless silver deposition. In this approach, a PDA thin film deposited on a polydimethylsiloxane (PDMS) flake is used to cover the substrate carrying LFPs and then gently peeled off. During this cover-separation process, PDA film is interfacially transferred from PDMS to the LFP ridges on the substrate in a spatially selective manner, leaving behind a complementary (negative) LFP pattern on the PDMS flake. Upon PDA-catalyzed electroless silver deposition, positive and negative LFP patterns are imaged on the original substrate and PDMS flake, respectively. This approach relies on the remarkably different adhesion energy of PDA on fingerprint sweat and PDMS and is applicable to fresh and aged LFPs on most nonporous substrates.

Mussel inspired polydopamine (PDA) film has attracted great interest as a versatile functional coating for biomolecule immobilization in various bio-related devices. However, the details regarding the interaction between a protein and PDA film remain unclear. Particularly, there is very limited knowledge regarding the protein immobilization on PDA film, even though it is of essential importance in various fields. The situation is even more complicated if considering the fact that quite a number of approaches (e.g., different oxidizing reagent, buffer pH, grown time, grown media, etc.) have been developed to grow PDA films. In this work, protein attachment on PDA film was systematically investigated by using the real-time and label-free surface plasmon resonance (SPR) technique. The kinetics of protein-PDA interaction was explored and the influence of buffer pH and deposition media on the protein attachment was studied. Fluorescent protein microarray was further printed on PDA-coated glass slides for quantitative investigations and together with SPR data, the interesting fluorescence quenching phenomenon of PDA film was revealed. This work may deepen our understanding on the PDA-protein interaction and offer a valuable guide for efficient protein attachment on PDA film in various bio-related applications.

The transition metal iron (Fe) has attracted particular interest in pursuit of low-cost oxygen reduction reaction (ORR) electrocatalysts. Carbon-supported iron oxides and oxyhydroxides have demonstrated promising ORR catalytic activities, but there is limited knowledge regarding the influence of iron species types and their crystalline phases on their ORR activities. In this paper we synthesized four iron/graphene composites with iron oxides (α-Fe2O3, Fe3O4) and oxyhydroxides (α-FeOOH, and α/γ-FeOOH) supported on graphene oxide (GO), and systematically investigated their ORR behaviors. It is found that decorating GO with iron oxides and oxyhydroxides can dramatically improve the ORR activity of pristine GO in alkaline solution in terms of onset potential and current density, and the α-Fe2O3/GO exhibits the highest ORR activity among all four composite materials investigated. This study unveils diverse ORR behaviors on GO-supported iron species, and explores the benchmark of their catalytic performances, and thus provides useful insights into the Fe-enabled high ORR activity for developing efficient transition metal-based ORR electrocatalysts.

Patterning metal films on various substrates is essentially important and yet challenging for developing a wide variety of innovative devices. We herein report a versatile approach to pattern metal (gold, silver, or copper) films on arbitrary substrates by using the bio-inspired polydopamine (PDA) thin film as a UV-sensitive adhesive layer for electroless deposition. The PDA film is able to be formed on virtually any solid surfaces under mild condition, and its rich catechol groups allow for electroless deposition of metal films with high adhesion stability. Upon UV irradiation, spatially selective oxidation of PDA film occurs and the local metal deposition is inhibited, thus facilitating successful patterning of metal films. Considering its versatility and simplicity, this strategy may demonstrate great applications in manufacturing various innovative devices.

•Copper was found to be corroded quickly by mild 0.01 M PBS.•Free-standing Cu3(PO4)2 nanoflower was spontaneously formed.•Protein-Cu3(PO4)2 hybrid nanoflower was further synthesized.•The underlying chemistry was thoroughly investigated.We herein report the spontaneous interfacial reaction between copper foil with 0.01 M phosphate buffered saline (PBS) to form free-standing cupric phosphate (Cu3(PO4)2) nanoflowers at ambient temperature. The underlying chemistry was thoroughly investigated and it is found that the formation of nanoflower is synergistically caused by dissolved oxygen, chlorine ions and phosphate ions. Enzyme-Cu3(PO4)2 hybrid nanoflower was further prepared successfully by using an enzyme-dissolving PBS solution and the enzymes in the hybrid exhibit enhanced biological activity. This work provides a facile route for large-scale synthesis of hierarchical inorganic and functional protein-inorganic hybrid architectures via a simple one-step solution-immersion reaction without using either template or surfactant, thus offering great potential for biosensing application among others.

Colloidal noble metal-conducting polymer core–shell nanoparticles show promising applications in a wide diversity of areas, but it remains a great challenge to develop a convenient synthetic method allowing strict control over their size/dimension and facile modulation of their nanostructures. In this work, we report the synthesis of monodisperse gold dendrite@polypyrrole (AuD@PPy) core–shell nanoparticles with an eco-friendly one-step solution reaction by triggering oxidative polymerization of pyrrole with tetrachloroauric acid. As-prepared AuD@PPy nanoparticle is composed of a gold dendrite core coated by a thin PPy shell; the size and the thickness of the PPy shell could be adjusted by simply changing the pyrrole concentration. Benefiting from the protective effect of the PPy shell, the nanoparticles demonstrate enhanced catalytic durability toward the reductive reaction of methylene blue (MB) compared with the citrate-capped gold nanoparticles (AuNPs).

Surface plasmon resonance imaging (SPRi) is one of the powerful tools for immunoassays with advantages of label-free, real-time, and high-throughput; however, it often suffers from limited sensitivity. Herein we report a dual signal amplification strategy utilizing polydopamine (PDA) functionalization of reduced graphene oxide (PDA-rGO) nanosheets for sensitive SPRi immunoassay in serum. The PDA-rGO nanosheet is synthesized by oxidative polymerization of dopamine in a gentle alkaline solution in the presence of graphene oxide (GO) sheets and then is antibody-conjugated via a spontaneous reaction between the protein and the PDA component. In the dual amplification mode, the first signal comes from capture of the antibody-conjugated PDA-rGO to form sandwiched immunocomplexes on the SPRi chip, followed by a PDA-induced spontaneous gold reductive deposition on PDA-rGO to further enhance the SPRi signal. The detection limit as low as 500 pg mL–1 is achieved on a nonfouling SPRi chip with high specificity and a wide dynamic range for a model biomarker, carcinoembryonic antigen (CEA) in 10% human serum.