li Wei

Colorimetric Biosensing Using Smart Materials

In recent years, colorimetric biosensing has attracted much attention because of its low cost, simplicity, and practicality. Since color changes can be read out by the naked eye, colorimetric biosensing does not require expensive or sophisticated instrumentation and may be applied to field analysis and point-of-care diagnosis. For transformation of the detection events into color changes, a number of smart materials have been developed, including gold nanoparticles, magnetic nanoparticles, cerium oxide nanoparticles, carbon nanotubes, graphene oxide, and conjugated polymers. Here, we focus on recent developments in colorimetric biosensing using these smart materials. Along with introducing the mechanisms of color changes based on different smart materials, we concentrate on the design of biosensing assays and their potential applications in biomedical diagnosis and environmental monitoring.

Non-Enzymatic-Browning-Reaction: A Versatile Route for Production of Nitrogen-Doped Carbon Dots with Tunable Multicolor Luminescent Display

The non-enzymatic browning, namely Maillard reaction is commonly invoked to account for abiotic chemical transformations of organic matter. Here we report a new reaction pathway via the Maillard reaction to systematically synthesize a series of nitrogen-doped carbon dots (C-dots) with superhigh quantum yield (QY) and tunable multicolor luminescent displayment. The starting materials are glucose and the serial amino acid analogues which allow systemically controlling luminescent and physicochemical properties of C-dots at will. Unexpectedly, the as-prepared C-dots possess bright photoluminescence with QY up to 69.1% which is almost the highest ever reported, favorable biocompatibility, excellent aqueous and nonaqueous dispersibility, ultrahigh photostability, and readily functionalization. We have demonstrated that they are particularly suitable for multicolor luminescent display and long-term and real-time cellular imaging. Furthermore, the methodology is readily scalable to large yield, and can provide sufficient amount of C-dots for practical demands.

Extraordinary Physical Properties of Functionalized Graphene

Graphene has attracted much attention in recent years due to its extraordinary electronic, optical, magnetic, thermal, and mechanical properties. Despite continuing theoretical and experimental success, the unique physical properties of graphene remain underused and underappreciated. The key challenge in harnessing of the unique properties of graphene is the difficulty of reliable manipulation of well-dispersed graphene. Chemical and physical functionalization of graphene has become a focus of especial interest, because they can not only stabilize, but also induce new properties of graphene. This review summarizes the intriguing physical properties of chemically oxidized and noncovalently modified graphene, and graphene-based nanocomposites with polymer matrices or nanoparticles. Along with introducing the physical properties of functionalized graphene, their potential applications in diverse research areas are discussed.

Label‐Free Ultrasensitive Detection of Human Telomerase Activity Using Porphyrin‐Functionalized Graphene and Electrochemiluminescence Technique

Using porphyrin-functionalized graphene, we construct a PCR-free, low-cost, rapid, and electrochemiluminenscence (ECL) assay for detection of telomerase activity that has been demonstrated in six different cell lines and can be used as initial screening of G-quadruplex DNA binding agents and telomerase inhibitors. This ECL sensor shows highly sensitive for detection of telomerase with the detection limit as low as 10 HeLa cells mL(-1) .

Nanoceria-Triggered Synergetic Drug Release Based on CeO2-Capped Mesoporous Silica Host-Guest Interactions and Switchable Enzymatic Activity and Cellular Effects of CeO2

Herein, a pH stimuli-responsive vehicle for intracellular drug delivery using CeO2 capped mesoporous silica nanoparticles (MSN) is reported. β-Cyclodextrin-modified CeO2 nanoparticles could cap onto ferrocene-functionalized mesoporous silica through host-guest interactions. After internalization into A549 cells by a lysosomal pathway, the ferrocenyl moieties are oxidized to ferrocenium ions by CeO2 lids, which could trigger the uncapping of the CeO2 and cause the drugs release. Because of the pH-dependent toxicity, the CeO2 here behaves as a multi-purpose entity that not only acts as a lid but also exhibits a synergistic antitumor effect on cancer cells. Meanwhile, the cell protective effect of CeO2 nanoparticles alone is demonstrated, which ensures that the dissolved CeO2 nanoparticles can be non-toxic to normal cells.

Capillary electrochromatographic separation of basic compounds with bare silica as stationary phase

Abstract The feasibility of capillary electrochromatography (CEC) was demonstrated using capillary columns packed with 3-μm silica particles and a mobile phase of organic–aqueous buffer system. The retention mechanisms of basic compounds were explored. Preliminary results indicated that the separation of the basic compounds in the CEC system involved multiple retention mechanisms including reversed-phase, cation-exchange as well as normal-phase mechanisms. In addition, electrophoretic mobility of the solutes also contributed to retention. The effects of experimental parameters such as the volume fraction of the organic modifier, pH value and ionic strength of the buffer on the retention behaviours of the solutes were investigated. A comparison of differences between CEC and CE of separations was also discussed.

Chiral detection using reusable fluorescent amylose-functionalized graphene

By using DNA or a peptide as a common probe, graphene-based biosensing has made significant progress. However, to the best of our knowledge, a graphene-based chiral sensor has not been reported. Chiroselective recognition is perhaps the most subtle to achieve because of the similarity of the optical enantiomers. Therefore, besides using DNA or peptides as probes, developing graphene-based sensors with chiral selectivity is highly desirable. Here a reusable natural cheap polysaccharide, amylose-functionalized graphene was developed for highly sensitive and visual fluorescent chiral sensing. The detection sensitivity toward L-Trp is over 100-times higher than that of recently reported electrochemical sensors and colorimetric sensors. In comparison with commonly used DNA or peptides as a probe, natural amylose is more attractive because of its low cost, ready availability, simple manipulation and renewability. The specific selectivity for tryptophan (Trp) enantiomers towards other essential amino acids allows potential chiroselective analysis of Trp in complex samples such as biological fluids. This design can, in principle, be implemented for other slender target molecules that can form an inclusion complex with amylose.

Direct UV detection of underivatized amino acids using capillary electrophoresis with online sweeping enrichment

This is an original report proposed a CE method for direct analysis of the underivatized amino acids using UV detection with relatively higher sensitivity, which was based on coordination interactions between amino acids and Cu (II) ions. In addition, an online sweeping preconcentration technique was easily combined to improve the detection sensitivity. Satisfying separations of the amino acids were obtained under optimized conditions: 50 mmol/L CuSO4-0.05% HAc-H2O (pH 4.5), and the separation voltage of 15 kV. The LODs for the analytes ranged from 0.1 to 0.5 micromol/L. The linearity of detection for all analytes was two orders of magnitude with the correlation coefficients greater than 0.99. The repeatability was displayed with an RSD less than 3% for migration time and peak height (n = 5). Moreover, some amino acids in real samples of human saliva and green tea were analyzed by this direct UV detection CE method with acceptable sensitivity.

A facile and versatile approach for controlling electroosmotic flow in capillary electrophoresis via mussel inspired polydopamine/polyethyleneimine co-deposition.

Electroosmotic flow (EOF), which reveals the charge property of capillary inner surface, has an important impact on the separation performance and reproducibility of capillary electrophoresis (CE). In this study, a novel, facile and versatile method to achieve diverse and controllable EOF in CE was reported based on the co-deposition of mussel-inspired polydopamine (PDA) and branched polyethyleneimine (PEI) on the capillary inner surface as the hybrid functional coating. After these PDA/PEI co-deposited columns were reinforced by the post-incubation of FeCl3, various magnitude and direction of EOF in CE could be easily achieved by varying a number of preparation parameters, including the mass ratio of DA/PEI and the molecular weight of PEI (including PEI-600, PEI-1800, PEI-10000 and PEI-70000). The separation effectiveness and stability of the hybrid coated columns were verified by the analysis of aromatic acids and aniline derivatives. The results showed that the controllable and diverse EOF was important in enhancing the separation performance of the analytes. The baseline separation of all the five aromatic acids can be achieved in 7 min with high separation efficiency by using the PDA/PEI-600 co-deposited column with the mass ratio of 6:1. On the other hand, with the PDA/PEI-70000 co-deposited column with the mass ratio of 6:1, the aniline compounds were easily baseline separated within 10 min. By contrast, using the bare and PDA coated columns, the migration of the aromatic acids was very slow and the baseline separation of the aniline compounds cannot be obtained. Moreover, the co-deposited columns showed long lifetime and good stability. The relative standard deviations for intra-day, inter-day and capillary-to-capillary repeatability of the PDA/PEI-600 co-deposited column with the mass ratio of 6:1, which was reinforced by the post-incubation of FeCl3, were all lower than 5%.

Opposing enantiomers of tartaric acid anchored on a surface generate different insulin assemblies and hence contrasting cellular responses

Chirality plays a pivotal role in biomolecule recognition, which is one of the key aspects of cell responses to a biomaterial surface. Generally, the effects of the properties of a biomaterial surface on cellular responses are modulated by adsorbed proteins. Surface chemistry, such as charge and hydrophobicity, has a profound effect on protein adsorption. Nevertheless, chirality has been seldom considered in biomaterial surface chemistry. Herein, using the classical biogenic chiral molecules, D- and L-tartaric acid, assembled into monolayers as a model chiral surface, we reported for the first time that surface chirality modulated insulin assembly, including the dynamics of adsorption, kinetics of the conformational transition and fibril formation, on D- and L-surfaces and determined the cellular effect of insulin on neuronal PC12 cells. On the D-surface, insulin retained its bioactivity; however, on the L-surface, insulin formed amyloid fibrils with lost bioactivity. Previous reports have demonstrated that insulin can act as growth and neuronal differentiation factors. The chiral surfaces that were preassembled with insulin exhibited contrasting cellular behaviours in proliferation and differentiation. High proliferation and a high differentiation rate were observed for PC12 cells on the insulin-adsorbed D-surface, whereas neither proliferation nor differentiation were observed for PC12 cells on the insulin-adsorbed L-surface. Since protein surface adsorption is ubiquitous for tissue engineering and cell adhesion, our work provides new insights into engineering novel biomaterials by taking into account surface chirality. Surface chirality is important and may determine cell fate on a chiral surface.