Rijun Gui

Carbon nanomaterials-based electrochemical aptasensors

Carbon nanomaterials (CNMs) have attracted increasing attention due to their unique electrical, optical, thermal, mechanical and chemical properties. CNMs are extensively applied in electronic, optoelectronic, photovoltaic and sensing devices fields, especially in bioassay technology. These excellent properties significantly depend on not only the functional atomic structures of CNMs, but also the interactions with other materials, such as gold nanoparticles, SiO2, chitosan, etc. This review systematically summarizes applications of CNMs in electrochemical aptasensors (ECASs). Firstly, definition and development of ECASs are introduced. Secondly, different ways of ECASs about working principles, classification and construction of CNMs are illustrated. Thirdly, the applications of different CNMs used in ECASs are discussed. In this review, different types of CNMs are involved such as carbon nanotubes, graphene, graphene oxide, etc. Besides, the newly emerging CNMs and CNMs-based composites are also discoursed. Finally, we demonstrate the future prospects of CNMs-based ECASs, and some suggestions about the near future development of CNMs-based ECASs are highlighted.

Fabrication strategies, sensing modes and analytical applications of ratiometric electrochemical biosensors

Previously developed electrochemical biosensors with single-electric signal output are probably affected by intrinsic and extrinsic factors. In contrast, the ratiometric electrochemical biosensors (RECBSs) with dual-electric signal outputs have an intrinsic built-in correction to the effects from system or background electric signals, and therefore exhibit a significant potential to improve the accuracy and sensitivity in electrochemical sensing applications. In this review, we systematically summarize the fabrication strategies, sensing modes and analytical applications of RECBSs. First, the different fabrication strategies of RECBSs were introduced, referring to the analytes-induced single- and dual-dependent electrochemical signal strategies for RECBSs. Second, the different sensing modes of RECBSs were illustrated, such as differential pulse voltammetry, square wave voltammetry, cyclic voltammetry, alternating current voltammetry, electrochemiluminescence, and so forth. Third, the analytical applications of RECBSs were discussed based on the types of target analytes. Finally, the forthcoming development and future prospects in the research field of RECBSs were also highlighted.

Recent advances and future prospects in molecularly imprinted polymers-based electrochemical biosensors

Molecularly imprinted polymers (MIPs)-based electrochemical biosensors (ECBSs) have many advantages from MIPs and ECBSs, such as high selectivity and sensitivity, chemical/mechanical stability, reusability, low limit of detection, facile preparation and low cost. MIPs-based ECBSs attract much attention in medical diagnose, biological analysis, environmental monitoring, food safety evaluation, etc. Due to the capacity of highly specific recognition for target biomolecules, MIPs-based ECBSs have been smartly designed and extensively used for electrochemical sensing applications in recent years, exhibiting obvious superiority over other analytical techniques. In this review, firstly we systematically summarize the recent advances of MIPs-based ECBSs reported in recent years, referring to the preparation, structures and components of sensing systems. Secondly, we highlight the sensing applications for various significant biomolecules (proteins, antibiotics, pesticide, neurotransmitter, hormone, etc.), and demonstrate the sensing mechanism and detection performance. Finally, the rational summaries, present challenges and future prospects in the field of MIPs-based ECBSs have been discussed reasonably.

Facile synthesis of gold nanorods/hydrogels core/shell nanospheres for pH and near-infrared-light induced release of 5-fluorouracil and chemo-photothermal therapy

We described a facile synthesis of pH and near-infrared (NIR) light dual-sensitive core/shell hybrid nanospheres, consisting of gold nanorods (GNR) as the core and poly(N-isopropylacrylamide-co-methacrylic acid) as the shell, p(NIPAM-MAA). The resultant GNR/p(NIPAM-MAA) nanospheres showed a core/shell structure, with an average diameter of ∼110nm and a strong longitudinal surface plasmon band at NIR region. Due to the photothermal effect of GNR and pH/thermal-sensitive volume transition of p(NIPAM-MAA) hydrogels, the nanospheres with loading of 5-fluorouracil (5-FU) by electrostatic interactions were developed as a smart carrier for pH- and photothermal-induced release of 5-FU. Experimental results testified that the cumulative release of 5-FU from nanospheres was markedly increased in a mild acidic medium. Moreover, a NIR light (808nm) irradiation triggered a greater and faster release of 5-FU, which was further testified by relevant results from in vitro cytotoxicity assay, in vivo tumor growth inhibition and histological images of ex vivo tumor sections. These results revealed significant applications of GNR/p(NIPAM-MAA) nanospheres in controlled release of anticancer agents and photothermal ablation therapy of tumor tissues, accompanied by synergistic effect of chem-photothermal therapy.

Carrot-derived carbon dots modified with polyethyleneimine and nile blue for ratiometric two-photon fluorescence turn-on sensing of sulfide anion in biological fluids

In this article, a facile and green synthesis of carbon dots (CDs) was developed by using natural carrot as new carbon source. After direct hydrothermal carbonization for 5h at 180°C, CDs were prepared facilely. Then, CDs were conjugated with polyethyleneimine (PEI) and Nile Blue (NB) chloride to produce CDs/PEI/NB nanocomposites under electrostatic interactions. Upon excitation at 800nm, two-photon fluorescence (TPF) of the nanocomposites was observed, with TPF peaks of CDs at 415nm and NB at 675nm. The addition of Cu2+ could lead to TPF quenching of CDs via inner filter effect, but hardly any impacted on TPF of NB. Afterward, the added S2- combined with Cu2+ to form stable species that caused the separation of Cu2+ from CDs surface and the TPF recovery of CDs, with negligible effects on TPF of NB. Herein, a new CDs-based ratiometric TPF turn-on probe of S2- was developed and showed a good linear relationship (R2 =0.9933) between ratiometric TPF intensity (I415/I675) and S2- concentration (0.1-8.0μM), with a low detection limit of 0.06μM. This probe was highly selective and sensitive toward S2- over potential interferences in real biological fluids, with high detection recoveries.

CuS nanocrystal@microgel nanocomposites for light-regulated release of dual-drugs and chemo-photothermal synergistic therapy in vitro

In this article, we described the synthesis of novel light-sensitive inorganic@organic core/shell nanocomposites that consisted of CuS nanocrystals as the core and a poly(N-isopropylacrylamide)-graft-chitosan (PNIPAM-g-CS) microgel as the shell. The CuS@PNIPAM-g-CS nanocomposites were synthesized by temperature-tunable copolymerization of NIPAM and CS in the presence of CuS nanocrystals (∼5.4 nm). The nanocomposites showed an average diameter of ∼56 nm and a strong longitudinal surface plasmon band in the near-infrared (NIR) region. Due to the photothermal effect of CuS under NIR light (980 nm) irradiation, the nanocomposites presented photothermal-sensitive volume shrinkage of the PNIPAM-g-CS microgel. After loading of doxorubicin (Dox), the nanocomposites were utilized as versatile nanocarriers for photothermal-induced release of Dox. After loading of Dox, nitric oxide (NO) photodonors (RBS) were then loaded into nanocomposites to fabricate Dox/RBS dual-loading CuS@PNIPAM-g-CS nanocarriers. Upon visible light (365 nm) irradiation, the nanocarriers could release NO due to the photolysis of RBS. Experimental results implied that NIR and visible light, respectively, triggered the release of Dox and NO from the nanocarriers. Together with the photothermal effect of CuS, the nanocarriers simultaneously realized the light-triggered release of dual-drugs and synergistic chem-photothermal therapy to cancer cells in vitro.

An electrochemical sensor for the sensitive detection of rutin based on a novel composite of activated silica gel and graphene

In this paper, a novel activated silica gel (ASiG)–graphene (G) composite was initially fabricated via a simple sonication-induced assembly and used as the substrate material to prepare an electrochemical sensor (ASiG/G/GCE) for the sensitive determination of rutin. Morphology and electrochemical properties of the composite were investigated by transmission electron microscopy (TEM), chronocoulometry, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Experimental results revealed that the ASiG/G composite induced a remarkable increase of the redox currents of rutin, which could be attributed to the high surface area and excellent electric conductivity of G, as well as the strong accumulation efficiency of ASiG toward rutin. The peak current from DPV is linearly dependent on the rutin concentration in a range of 0.001 to 1.2 μmol L−1 with a detection limit of 3.3 nmol L−1. The ASiG/G/GCE also exhibited good selectivity and acceptable reproducibility. Moreover, the ASiG/G/GCE was successfully applied to the fast determination of rutin in medicine tablets and human plasma with satisfactory recoveries. Therefore, the present work offers a new way to broaden the analytical applications of functionalized graphene in pharmaceutical research.

Glycerol-regulated facile synthesis and targeted cell imaging of highly luminescent Ag2Te quantum dots with tunable near-infrared emission.

In this work, highly luminescent and emission tunable Ag2Te quantum dots (QDs) were facilely prepared by using water-dispersed glycerol as viscous solvent and CH3COOAg/Na2TeO3 as Ag/Te precursors. Viscous glycerol was utilized to slow the nucleation and growth of QDs at 200°C, and enabled the isolation of QDs with different emission wavelengths. Experimental results revealed that the as-prepared Ag2Te QDs exhibited tunable near-infrared emission from 930 to 1084nm, high photoluminescence (PL) quantum yields (QYs, more than 20%), good photostability and low cytotoxicity. After surface coating of a thin silica shell (∼1.4nm), the resulting NH2 terminated Ag2Te@SiO2-NH2 displayed enhanced PL QYs, higher photostability and biocompatibility when compared with the original Ag2Te QDs. Through a facile carboxy-amine coupling, folic acid (FA) was grafted with Ag2Te@SiO2-NH2 to form Ag2Te@SiO2-FA nanocomposites, which were used for targeted PL imaging of folate receptor over-expressed tumor cells.

Aptamer and 5-fluorouracil dual-loading Ag2S quantum dots used as a sensitive label-free probe for near-infrared photoluminescence turn-on detection of CA125 antigen

In this article, Ag2S quantum dots (QDs) were prepared by a facile aqueous synthesis method, using thiourea as a new sulfur precursor. Based on electrostatic interactions, 5-fluorouracil (5-Fu) was combined with the aptamer of CA125 antigen to fabricate aptamer/5-Fu complex. The surface of as-prepared Ag2S QDs was modified with polyethylenimine, followed by combination with the aptamer/5-Fu complex to form Ag2S QDs/aptamer/5-Fu hybrids. During the combination of Ag2S QDs with aptamer/5-Fu complex, near-infrared (NIR) photoluminescence (PL) of QDs (peaked at 850nm) was markedly reduced under excitation at 625nm, attributed to photo-induced electron transfer from QDs to 5-Fu. However, the addition of CA125 induced obvious NIR PL recovery, which was ascribed to the strong binding affinity of CA125 with its aptamer, and the separation of aptamer/5-Fu complex from the surface of QDs. Hence, the Ag2S QDs/aptamer/5-Fu hybrids were developed as a novel NIR PL turn-on probe of CA125. In the concentration range of [CA125] from 0.1 to 106ngmL-1, there were a good linear relationship between NIR PL intensities of Ag2S QDs and Log[CA125], and a low limit of detection of 0.07ngmL-1. Experimental results revealed the highly selective and sensitive NIR PL responses of this probe to CA125, over other potential interferences. In real human body fluids, this probe also exhibited superior analytical performance, together with high detection recoveries.

Lable-free quadruple signal amplification strategy for sensitive electrochemical p53 gene biosensing

A versatile label-free quadruple signal amplification biosensing platform for p53 gene (target DNA) detection was proposed. The chitosan-graphene (CS-GR) modified electrode with excellent electron transfer ability could provide a large specific surface for high levels of AuNPs-DNA attachment. The large amount of AuNPs could immobilize more capture probes and enhance the electrochemical signal with the excellent electrocatalytic activity. Furthermore, with the assist of N.BstNB I (the nicking endonuclease), target DNA could be reused and more G-quadruplex-hemin DNAzyme could be formed, allowing significant signal amplification in the presence of H2O2. Such strategy can enhance the oxidation-reduction reaction of adsorbed methylene blue (MB) and efficiently improve the sensitivity of the proposed biosensor. The morphologies of materials and the stepwise biosensor were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cyclic voltammetry (CV). Differential pulse voltammetry (DPV) signals of MB provided quantitative measures of the concentrations of target DNA, with a linear calibration range of 1.0 × 10(-15)-1.0 × 10(-9)M and a detection limit of 3.0 × 10(-16)M. Moreover, the resulting biosensor also exhibited good specificity, acceptable reproducibility and stability, indicating that the present strategy was promising for broad potential application in clinic assay.