Shanni Hong

Label-free detection of Pb2+ based on aggregation-induced emission enhancement of Au-nanoclusters

Interestingly, the glutathione capped Au-nanoclusters presented here showed a unique optical performance compared with their homological AuNPs with larger size. The luminescence intensity of the AuNCs could be enhanced due to the formation of aggregates. The AuNCs were then employed as a visual probe for the detection of Pb2+ based on the aggregation-induced emission enhancement (AIEE) property of the AuNCs. When the luminous glutathione capped AuNCs probes encountered Pb2+ ions, they rapidly formed aggregates through GSH–Pb2+ interaction in 1 minute, resulting in an enhanced luminescence intensity. The enhanced luminescence intensities showed a linear dependence on the concentrations of Pb2+ with satisfactory selectivity towards 12 kinds of divalent metal ions. More importantly, the probe can also be used for on-site testing to inspect Pb2+ contamination by using a portable UV flashlight.

In vitro selection of DNA aptamers against renal cell carcinoma using living cell-SELEX

Renal cell carcinoma (RCC) is the most common form of kidney cancer with poor prognosis. Early diagnosis of RCC would significantly improve patient prognosis and quality of life. In this work, we developed new aptamer probes for RCC by using cell-SELEX (systematic evolution of ligands by exponential enrichment) only after 12 rounds of selection, in which a clear cell renal cell carcinoma (ccRCC) cell line 786-O was used as target cell, and embryonic kidney cell line 293T as negative control cell. The selected aptamers were subjected to flow cytometry and laser confocal fluorescence microscopy to evaluate their binding affinity and selectivity. The dissociation constant Kd values of four selected aptamers are all in the nanomolar range. Aptamer W786-1 with the best binding affinity and a Kd value of 9.4 ± 2.0nM was further optimized and its truncated sequence W786-1S showed considerable affinity to 786-O cells. The proteinase and temperature treatment experiment indicated that W786-1 could recognize the target 786-O cells through surface proteins, and remain good binding affinity and excellent selectivity under physiological conditions. Therefore, on the basis of its excellent targeting properties and functional versatility, W786-1 holds great potential to be used as a molecular probe for identifying and targeting RCC.

DNA sequence-dependent fluorescence of doxorubicin for turn-on detection of biothiols in human serum.

Doxorubicin (Dox) is a DNA-targeting anthracycline antibiotic active against a wide spectrum of cancers. The interaction between Dox and double-stranded DNA (dsDNA) was used to load Dox using DNA duplexes as carriers. More importantly, the interesting DNA sequence-dependent fluorescence response of Dox could be exploited in the design of efficient Dox release systems and efficient fluorescence sensors. In this work, we demonstrated that separate introduction of G and C bases into T-rich single-stranded DNA (ssDNA) sequences afforded the best discrimination of Dox binding between dsDNA and ssDNA. For the first time, we successfully utilized this interesting DNA sequence-dependent fluorescence response of Dox as a signal transduction mechanism for the sensitive detection of biothiols in human serum. Cysteine, homocysteine, and glutathione were detected at as low as 26 nM, 37 nM, and 29 nM, respectively. The biosensors exhibited not only good selectivity, stability, and sensitivity in aqueous solutions but also a sensitive response in human serum, demonstrating their potential for diagnosis.

Label-free DNA-based biosensors using structure-selective light-up dyes

Label-free biosensors (LFBs) have demonstrated a great potential in cost-effective applications, and most of the DNA-based LFBs are based on the principle of binding-induced structural transformation. This review is a collection of the latest reported studies, which have employed structure-selective nucleic acid dyes for the development of DNA-based LFBs. The collections in this review have been structured based on the selective binding of dyes towards specific DNA conformations, including single-stranded DNA, double-stranded DNA, triplex DNA, i-motifs and G-quadruplexes. The newest studies of employing versatile nucleases, fascinating nanomaterials, logic gates and cascades, DNA junctions and nanostructures have also been collected as examples. It is predicted that the imperative requirement for ultrahigh sensitivity, intelligent analysis, reliable detection, portable and fast assay would force the LFB development in a stimulative and continuous way.

DNA Triplexes-Guided Assembly of G-Quadruplexes for Constructing Label-free Fluorescent Logic Gates.

Assembly of G-quadruplexes guided by DNA triplexes in a controlled manner is achieved for the first time. The folding of triplex sequences in acidic conditions brings two separated guanine-rich sequences together and subsequently a G-quadruplex structure is formed in the presence of K(+) . Based on this novel platform, label-free fluorescent logic gates, such as AND, INHIBIT, and NOR, are constructed with ions as input and the fluorescence of a G-quadruplex-specific fluorescent probe NMM as output.

Functional Hyperbranched Polylysine as Potential Contrast Agent Probes for Magnetic Resonance Imaging

Researchers have never stopped questing contrast agents with high resolution and safety to overcome the drawbacks of small-molecule contrast agents in clinic. Herein, we reported the synthesis of gadolinium-based hyperbranched polylysine (HBPLL-DTPA-Gd), which was prepared by thermal polymerization of l-lysine via one-step polycondensation. After conjugating with folic acid, its potential application as MRI contrast agent was then evaluated. This contrast agent had no obvious cytotoxicity as verified by WST assay and H&E analysis. Compared to Gd(III)-diethylenetriaminepentaacetic acid (Gd-DTPA) (r1 = 4.3 mM(-1) s(-1)), the FA-HBPLL-DTPA-Gd exhibited much higher longitudinal relaxivity value (r1 = 13.44 mM(-1) s(-1)), up to 3 times higher than Gd-DTPA. The FA-HBPLL-DTPA-Gd showed significant signal intensity enhancement in the tumor region at various time points and provided a long time window for MR examination. The results illustrate that FA-HBPLL-DTPA-Gd will be a potential candidate for tumor-targeted MRI.

Building a chimera of aptamer–antisense oligonucleotide for silencing galectin-1 gene

Galectin-1 is closely related with immune systems, and its overexpression may cause tumor metastasis. Owing to the better stability of antisense oligonucleotides than siRNA, we constructed a chimera of aptamer–antisense oligonucleotide (Apt–AS) for silencing the galectin-1 gene specifically. For studying the endocytosis pathways of Apt–AS by aptamer targeted delivery, we marked the 3′ terminus of Apt–AS with Alexa Flour 488 (Apt–AS488) so as to trace the pathways through the confocal microscope. Furthermore, Apt–AS was used to silence the expression of galectin-1. The results showed Apt–AS entered cells by a caveolae mediated endocytosis pathway, and the aptamer–antisense chimeras did not impair the antisense gene silencing efficiency. Moreover Apt–AS could improve the cellular uptake and selectively entered cells.

Self-assembled RNAi nanoflowers via rolling circle transcription for aptamer-targeted siRNA delivery

To deliver siRNA efficiently, prevailing conventional lipid or polymer encapsulation often needs multi-step compounding methods, which may inevitably introduce cationic or other components and may lead to cytotoxicity or an immune response. Herein, we present a novel enzymatic synthetic approach to produce tumor-targetable RNAi nanoflowers. The RNAi nanoflowers are mainly composed of multiple tandem copies of siRNA precursors by rolling circle transcription (RCT), and produce large amounts of siRNA to silence Bcl-2 gene expression after cellular uptake, which can overcome the problem of low loading capacity. In particular, the RNAi microspheres (RNAi-MS) were condensed into nanosized complexes (RNAi nanospheres, RNAi-NS) by cholesterol-modified DNA strands without the assistance of polycationic agents. RNAi-NS are entirely composed of nucleic acid, giving them lower cytotoxicity and immunogenicity, which can be caused by synthetic polycationic reagents. In addition, the RNAi nanoflowers can also integrate DNA aptamers that bind specifically to target membrane proteins for cell-targeting. Therefore, thousands of copies of siRNA will be delivered to cells specifically, and this RNAi nanoflower system will have great potential for siRNA delivery and biomedical applications.

A novel photoelectrochemical aptasensor based on the modulation of a dye sensitized TiO2 photoelectrode

An N719 dye labeled short DNA chain is introduced onto the surface of a TiO2 photoelectrode by hybridizing with a pre-immobilized thrombin aptamer to enhance the photocurrent response. After incubating with thrombin, both the dye labeled chain releasing from the photoelectrode and the bound thrombin blocking the electron transfer resulted in a decreased photocurrent.