Herein, we report a combined electrochemical and ESI-MS study of the enzymatic hydrolysis efficiency of DNA self-assembled monolayers (SAMs) on gold, platform systems for understanding nucleic acid surface chemistry, and for constructing DNA-based biosensors. Our electrochemical approach is based on the comparison of the amounts of surface-tethered DNA nucleotides before and after exonuclease I (Exo I) incubation using electrostatically bound [Ru(NH3)6]3+ as redox indicators. It is surprising to reveal that the hydrolysis efficiency of ssDNA SAMs does not depend on the packing density and base sequence, and that the cleavage ends with surface-bound shorter strands (9–13 mers). The ex-situ ESI-MS observations confirmed that the hydrolysis products for ssDNA SAMs (from 24 to 56 mers) are dominated with 10–15 mer fragments, in contrast to the complete digestion in solution. Such surface-restrained hydrolysis behavior is due to the steric hindrance of the underneath electrode to the Exo I/DNA binding, which is essential for the occurrence of Exo I-catalyzed processive cleavage. More importantly, we have shown that the hydrolysis efficiency of ssDNA SAMs can be remarkably improved by adopting long alkyl linkers (locating DNA strands further away from the substrates).

We report herein a heat-triggered precursor slow releasing route for the one-pot synthesis of ultrathin ZnSe nanowires (NWs), which relies on the gradual dissolving of Se powder into oleylamine containing a soluble Zn precursor under heating. This route allows the reaction system to maintain a high monomer concentration throughout the entire reaction process, thus enabling the generation of ZnSe NWs with diameter down to 2.1 nm and length approaching 400 nm. The size-dependent optical properties and band-edge energy levels of the ZnSe NWs were then explored in depth by UV-visible spectroscopy and cyclic voltammetry, respectively. Considering their unique absorption properties, these NWs were specially utilized for fabricating photoelectrochemical-type photodetectors (PDs). Impressively, the PDs based on the ZnSe NWs with diameters of 2.1 and 4.5 nm exhibited excellent responses to UVA and near-visible light, respectively: both possessed ultrahigh on/off ratios (5150 for UVA and 4213 for near-visible light) and ultrawide linear response ranges (from 2.0 to 9000 μW cm−2 for UVA and 5.0 to 8000 μW cm−2 for near-visible light). Furthermore, these ZnSe NWs were selectively doped with various amounts of Mn2+ to tune their emission properties. As a result, ZnSe NW film-based photochromic cards were creatively developed for visually detecting UVA and near-visible radiation.

On-site oral fluid testing for drugs of abuse has become prominent in order to take immediate administrative action in an enforcement process. Herein, we report a DVD technology-based indirect competitive immunoassay platform for the quantitative detection of drugs of abuse. A microfluidic approach was adapted to prepare multiplex immunoassays on a standard DVD-R, an unmodified multimode DVD/Blu-Ray drive to read signal, and a free disc-quality analysis software program to process the data. The DVD assay platform was successfully demonstrated for the simultaneous, quantitative detection of drug candidates (morphine and cocaine) in oral fluids with high selectivity. The detection limit achieved was as low as 1.0 ppb for morphine and 5.0 ppb for cocaine, comparable with that of standard mass spectrometry and ELISA methods.

Monodispersed and ultrastable colloidal ZnS nanospheres (NPs) composed of tiny nanoparticles were successfully synthesized by using a limited ligand-induced in situ aggregation strategy. With such a strategy, the whole size as well as the particle size of those ZnS NPs could be tuned simultaneously by appropriately varying the reaction conditions. Three representative ZnS NP samples with different sphere sizes and particle sizes were thus obtained, which were all proven to possess rather large surface areas, robust structures and excellent colloidal stability. Furthermore, the photocatalytic activities of the as-prepared ZnS NPs toward the photodegradation of eosin B, methylene blue and their binary mixture were explored respectively. An interesting size-dependent degradation performance associated with the ZnS NPs was observed in all the photodegradation cases. Finally, their degradation mechanism was fully elucidated according to the control experiments under different atmospheres in combination with the related energy level information. We believe that the control strategy for tuning the fine and whole structures of spherical nanostructures in a synergistic manner together with the structure-dependent photodegradation performance revealed herein will definitely benefit the fabrication of highly efficient photocatalysts as well as the nanocomplexes with hierarchical architectures.

In this paper, we report a novel DNA molecular beacon (MB)-based plastic biochip platform for scanometric detection of a range of analytical targets. Hairpin DNA strands, which are dually modified with amino and biotin groups at their two ends are immobilized on a disposable plastic (polycarbonate) substrate as recognition element and gold nanoparticle-assisted silver-staining as signal reading protocol. Initially, the immobilized DNA probes are in their folded forms; upon target binding the hairpin secondary structure of the probe strand is “forced” open (i.e., converted to the unfolded state). Nanogold-streptavidin conjugates can then bind the terminal biotin groups and promote the deposition of rather large silver particles which can be either directly visualized or quantified with a standard flatbed scanner. We demonstrate that with properly designed probe sequences and optimized preparation conditions, a range of molecular targets, such as DNA strands, proteins (thrombin) and heavy metal ions (Hg2+), can be detected with high sensitivity and excellent selectivity. The detection can be done in both standard physiological buffers and real world samples. This constitutes a platform technology for performing rapid, sensitive, cost-effective, and point-of-care (POC) chemical analysis and medical diagnosis.Keywords: DNA molecular beacon; medical diagnosis; plastic biochip; scanometric detection; target-induced conformation switching

In this paper, we have elucidated the fundamental principle of employing CV to investigate the band structures of semiconductor nanocrystals (SNCs), and have also built up an optimal protocol for performing such investigation. By utilizing this protocol, we are able to obtain well-defined and characteristic electrochemical redox signals of SNCs, which allows us to intensively explore the influences of the particle size, the surface ligand and particle composition on the band structures of CdSe, CdTe and their alloy nanocrystals. The size-, ligand- and composition-dependent band structures of CdSe and CdTe nanocrystals (NCs) have therefore been mapped out, respectively, which are generally consistent with the previous theoretical and experimental reports. We believe that the optimal protocol and the original results regarding electrochemical characterization of SNCs demonstrated in this paper will definitely benefit the better understanding, modulation and application of the unique electronic and optical properties of SNCs.

Traditional methods of disease diagnosis are both time-consuming and labor-intensive, and many tests require expensive instrumentation and trained professionals, which restricts their use to biomedical laboratories. Because patients can wait several days (even weeks) for the results, the consequences of delayed treatment could be disastrous. Therefore, affordable and simple point-of-care (POC) biosensor devices could fill a diagnostic niche in the clinic or even at home, as personal glucose meters do for diabetics. These devices would allow patients to check their own health conditions and enable physicians to make prompt treatment decisions, which could improve the chances for rapid recovery and cure.Compact discs (CDs) provide inexpensive substrate materials for the preparation of microarray biochips, and conventional computer drives/disc players can be adapted as precise optical reading devices for signal processing. Researchers can employ the polycarbonate (PC) base of a CD as an alternative substrate to glass slides or silicon wafers for the preparation of microanalytical devices. Using the characteristic optical phenomena occurring on the metal layer of a CD, researchers can develop biosensors based on advanced spectroscopic readout (interferometry or surface plasmon resonance). If researchers integrate microfluidic functions with CD mechanics, they can control fluid transfer through the spinning motion of the disc, leading to “lab-on-a-CD” devices.Over the last decade, our laboratory has focused on the construction of POC biosensor devices from off-the-shelf CDs or DVDs and standard computer drives. Besides the initial studies of the suitability of CDs for surface and materials chemistry research (fabrication of self-assembled monolayers and oxide nanostructures), we have demonstrated that an ordinary optical drive, without modification of either the hardware or the software driver, can function as the signal transducing element for reading disc-based bioassays quantitatively.In this Account, we first provide a brief introduction to CD-related materials chemistry and microfluidics research. Then we describe the mild chemistry developed in our laboratory for the preparation of computer-readable biomolecular screening assays: photochemical activation of the polycarbonate (PC) disc surface and immobilization and delivery of probe and target biomolecules. We thoroughly discuss the analysis of the molecular recognition events: researchers can “read” these devices quantitatively with an unmodified optical drive of any personal computer. Finally, and critically, we illustrate our digitized molecular diagnosis approach with three trial systems: DNA hybridization, antibody–antigen binding, and ultrasensitive lead detection with a DNAzyme assay. These examples demonstrate the broad potential of this new analytical/diagnostic tool for medical screening, on-site food/water safety testing, and remote environmental monitoring.

A novel template-assisted deposition and etching strategy is proposed in this paper for preparing IrO2 nanotube arrays on ITO substrates, i.e., electrodepositing IrO2 nanoparticles onto ZnO nanorod surfaces to produce IrO2-coated core–shell nanorod arrays, and followed by wet chemical etching the ZnO nanorods away to generate IrO2 nanotube arrays. Well-aligned IrO2 nanotube arrays with high purity and uniform size are produced by using this synthetic strategy. Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) are employed to examine the morphology, fine structure and composition of the IrO2 nanotube arrays intensively. Furthermore, electrocatalytic water oxidization experiments are performed to assess the catalytic performance of the as-prepared IrO2 nanotube arrays toward oxygen evolution reaction (OER). The IrO2 nanotube arrays have been found to possess an excellent catalytic performance: high turnover frequency (3.3 s−1 for TOF at 1.2 V versus Ag/AgCl), low oxygen evolution overpotential (η = 0.15 V) and good catalytic stability (55% catalytic activity remaining after undergoing 400 times potential cycles).Graphical abstractWell-aligned IrO2 nanotube arrays are fabricated by using a template-assisted deposition and etching strategy, which demonstrates good catalytic performance toward oxygen evolution reaction (OER).Highlights► A simple an general strategy for fabricating nanotube arrays. ► Well-aligned IrO2 nanotube arrays on conductive substrates. ► Excellent catalytic performance toward oxygen evolution reaction (OER).

A novel ligand tuning strategy for the synthesis and assembly of ZnTe nanocrystals is proposed in this paper: a specific ligand is selected to work with the reaction system to regulate (passivate or activate) the reactivity of zinc precursors, as well as the growth and the assembly of resulting nanocrystals in a coordinate way. By utilization of this strategy, high-quality ZnTe nanodots, branched-nanorods (including nanotetrapods), nanowires and microspheres are obtained. Furthermore, by using ZnTe microspheres as building blocks, ordered two-dimensional (2D) and three-dimensional (3D) arrays and well-defined hollow microspheres are fabricated. The size, morphology, and crystal structure of as-prepared ZnTe nanocrystals are well characterized. The underlying mechanisms for ligand-tuned synthesis and assembly of ZnTe nanocrystals are also intensively discussed. Finally, the shape-dependent optical, structural, and electrochemical properties of those ZnTe nanocrystals are systemically investigated; their band edge positions are studied by cyclic voltammetry.

Monodispersed and ultrastable colloidal ZnS nanospheres (NPs) composed of tiny nanoparticles were successfully synthesized by using a limited ligand-induced in situ aggregation strategy. With such a strategy, the whole size as well as the particle size of those ZnS NPs could be tuned simultaneously by appropriately varying the reaction conditions. Three representative ZnS NP samples with different sphere sizes and particle sizes were thus obtained, which were all proven to possess rather large surface areas, robust structures and excellent colloidal stability. Furthermore, the photocatalytic activities of the as-prepared ZnS NPs toward the photodegradation of eosin B, methylene blue and their binary mixture were explored respectively. An interesting size-dependent degradation performance associated with the ZnS NPs was observed in all the photodegradation cases. Finally, their degradation mechanism was fully elucidated according to the control experiments under different atmospheres in combination with the related energy level information. We believe that the control strategy for tuning the fine and whole structures of spherical nanostructures in a synergistic manner together with the structure-dependent photodegradation performance revealed herein will definitely benefit the fabrication of highly efficient photocatalysts as well as the nanocomplexes with hierarchical architectures.

In this paper, we have elucidated the fundamental principle of employing CV to investigate the band structures of semiconductor nanocrystals (SNCs), and have also built up an optimal protocol for performing such investigation. By utilizing this protocol, we are able to obtain well-defined and characteristic electrochemical redox signals of SNCs, which allows us to intensively explore the influences of the particle size, the surface ligand and particle composition on the band structures of CdSe, CdTe and their alloy nanocrystals. The size-, ligand- and composition-dependent band structures of CdSe and CdTe nanocrystals (NCs) have therefore been mapped out, respectively, which are generally consistent with the previous theoretical and experimental reports. We believe that the optimal protocol and the original results regarding electrochemical characterization of SNCs demonstrated in this paper will definitely benefit the better understanding, modulation and application of the unique electronic and optical properties of SNCs.