Daoqing Fan

Colorimetric Strategy for Highly Sensitive and Selective Simultaneous Detection of Histidine and Cysteine Based on G-Quadruplex-Cu(II) Metalloenzyme

In this present work, we proposed a colorimetric strategy for simultaneous detection of histidine and cysteine based on G-quadruplex-Cu(II) metalloenzyme for the first time. Because of the adding of histidine or cysteine, the formation of G-quadruplex-Cu(II) metalloenzyme will be disturbed, thus the catalytic activity to TMB-H2O2 reaction is inversely proportional to the concentration of histidine or cysteine. With this strategy, the limit of detection in experimental measurement for histidine and cysteine is 10 nM and 5 nM, respectively, which are both lower than previous colorimetric arrays. With the help of NEM, cysteine is alkylated and the reaction between Cu(2+) is inhibited, so the selectivity can also be guaranteed. The cost is quite low since the developed array is label free and enzyme free by using low-cost DNA and Cu(2+). More importantly, the colorimetric detection operation is very simple without any further modification process.

Highly sensitive and specific colorimetric detection of cancer cells via dual-aptamer target binding strategy

Simple, rapid, sensitive and specific detection of cancer cells is of great importance for early and accurate cancer diagnostics and therapy. By coupling nanotechnology and dual-aptamer target binding strategies, we developed a colorimetric assay for visually detecting cancer cells with high sensitivity and specificity. The nanotechnology including high catalytic activity of PtAuNP and magnetic separation & concentration plays a vital role on the signal amplification and improvement of detection sensitivity. The color change caused by small amount of target cancer cells (10 cells/mL) can be clearly distinguished by naked eyes. The dual-aptamer target binding strategy guarantees the detection specificity that large amount of non-cancer cells and different cancer cells (10(4) cells/mL) cannot cause obvious color change. A detection limit as low as 10 cells/mL with detection linear range from 10 to 10(5) cells/mL was reached according to the experimental detections in phosphate buffer solution as well as serum sample. The developed enzyme-free and cost effective colorimetric assay is simple and no need of instrument while still provides excellent sensitivity, specificity and repeatability, having potential application on point-of-care cancer diagnosis.

Cascaded multiple amplification strategy for ultrasensitive detection of HIV/HCV virus DNA

Ultrasensitive detection of HIV and HCV virus DNA is of great importance for early accurate diagnostics and therapy of HIV virus-infected patients. Herein, to our best knowledge, it is the first to use DNA cascaded multiple amplification strategy for ultrasensitive detection of HIV virus DNA with G-quadruplex-specific fluorescent or colorimetric probes as signal carriers. The developed strategy also exhibited universal applicability for HCV virus DNA detection. After reaction for about 4h, high sensitivity and specificity can be achieved at both fluorescent and colorimetric strategies (limit of detection (LOD) of 10 fM and 0.5pM were reached for fluorescent and colorimetric detection, respectively). And the single-based mismatched DNA even can be distinguished by naked eyes. It is believed that the cascaded multiple amplification strategy presents a huge advance in sensing platform and potential application in future clinical diagnosis.

Introducing Ratiometric Fluorescence to MnO2 Nanosheet-Based Biosensing: A Simple, Label-Free Ratiometric Fluorescent Sensor Programmed by Cascade Logic Circuit for Ultrasensitive GSH Detection

Glutathione (GSH) plays crucial roles in various biological functions, the level alterations of which have been linked to varieties of diseases. Herein, we for the first time expanded the application of oxidase-like property of MnO2 nanosheet (MnO2 NS) to fluorescent substrates of peroxidase. Different from previously reported fluorescent quenching phenomena, we found that MnO2 NS could not only largely quench the fluorescence of highly fluorescent Scopoletin (SC) but also surprisingly enhance that of nonfluorescent Amplex Red (AR) via oxidation reaction. If MnO2 NS is premixed with GSH, it will be reduced to Mn2+ and lose the oxidase-like property, accompanied by subsequent increase in SCs fluorescence and decrease in ARs. On the basis of the above mechanism, we construct the first MnO2 NS-based ratiometric fluorescent sensor for ultrasensitive and selective detection of GSH. Notably, this ratiometric sensor is programmed by the cascade logic circuit (an INHIBIT gate cascade with a 1 to 2 decoder). And a linear relationship between ratiometric fluorescent intensities of the two substrates and logarithmic values of GSHs concentrations is obtained. The detection limit of GSH is as low as 6.7 nM, which is much lower than previous ratiometric fluorescent sensors, and the lowest MnO2 NS-based fluorescent GSH sensor reported so far. Furthermore, this sensor is simple, label-free, and low-cost; it also presents excellent applicability in human serum samples.

A label-free colorimetric aptasensor for simple, sensitive and selective detection of Pt (II) based on platinum (II)-oligonucleotide coordination induced gold nanoparticles aggregation

Herein, a gold nanoparticles (AuNPs) based label-free colorimetric aptasensor for simple, sensitive and selective detection of Pt (II) was constructed for the first time. Four bases (G-G mismatch) mismatched streptavidin aptamer (MSAA) was used to protect AuNPs from salt-induced aggregation and recognize Pt (II) specifically. Only in the presence of Pt (II), coordination occurs between G-G bases and Pt (II), leading to the activation of streptavidin aptamer. Streptavidin coated magnetic beads (MBs) were used as separation agent to separate Pt (II)-coordinated MSAA. The residual less amount of MSAA could not efficiently protect AuNPs anymore and aggregation of AuNPs will produce a colorimetric product. With the addition of Pt (II), a pale purple-to-blue color variation could be observed by the naked eye. A detection limit of 150nM and a linear range from 0.6μM to 12.5μM for Pt (II) could be achieved without any amplification.

Simple, fast, label-free, and nanoquencher-free system for operating multivalued DNA logic gates using polythymine templated CuNPs as signal reporters

Boolean logic devices play a key role in both traditional and nontraditional molecular logic circuits. This kind of binary logic, in which each bit is coded by (0, 1), has only two output states—on or off (or high/low). Because of the finite computing capacity and variation, it is facing challenges from multivalued logic gates while processing high-density or uncertain/imprecise information. However, a low-cost, simple, and universal system that can perform different multivalued logic computations has not yet been developed, and remains a concept for further study. Herein, taking the ternary OR and INHIBIT logic gates as model devices, we present the fabrication of a novel simple, fast, label-free, and nanoquencher-free system for multivalued DNA logic gates using poly-thymine (T) templated copper nanoparticles (CuNPs) as signal reporters. The mixture of Cu2+ and ascorbic acid (AA) is taken as a universal platform for all ternary logic gates. Different kinds of poly-T strands and delicately designed complementary poly-adenine (A) strands are alternatively applied as ternary inputs to exhibit the ternary output states (low/0, medium/1, high/2). Notably, there are no nanoquenchers in this platform as poly-A strands can function as not only inputs but also efficient inhibitors of poly-T templated CuNPs. Moreover, all DNA are unlabeled single-strand DNA that do not need sophisticated labeling procedures or sequence design. The above design greatly reduces the operating time, costs, and complexity. More importantly, the ternary logic computations can be completed within 20 min because of the fast formation of CuNPs, and all of them share the same threshold values.

Tyramine Hydrochloride Based Label‐Free System for Operating Various DNA Logic Gates and a DNA Caliper for Base Number Measurements

DNA is believed to be a promising candidate for molecular logic computation, and the fluorogenic/colorimetric substrates of G-quadruplex DNAzyme (G4zyme) are broadly used as label-free output reporters of DNA logic circuits. Herein, for the first time, tyramine-HCl (a fluorogenic substrate of G4zyme) is applied to DNA logic computation and a series of label-free DNA-input logic gates, including elementary AND, OR, and INHIBIT logic gates, as well as a two to one encoder, are constructed. Furthermore, a DNA caliper that can measure the base number of target DNA as low as three bases is also fabricated. This DNA caliper can also perform concatenated AND-AND logic computation to fulfil the requirements of sophisticated logic computing.

An intelligent universal system yields double results with half the effort for engineering a DNA “Contrary Logic Pairs” library and various DNA combinatorial logic circuits

As an outstanding candidate of molecular logic computing, DNA logic computing has gained extensive advancements across diverse research areas. Nevertheless, current DNA logic gates with various functions are fragmentary nominated and always constructed separately due to their different operating-principles. Tedious/obligatory gates’ redesign/reoperation resulted in longer time, higher costs and lower computing efficiency. Herein, we, for the first time, propose the concept of “Contrary Logic Pairs” to systematically classify DNA gates with opposite functions into “positive^negative” gates (CLP = Pos^Neg). By utilizing two fluorescent substrates (Amplex Red, Scopoletin) of G-quadruplex DNAzyme as label-free signal-reporters, based solely on DNA hybridization, we fabricated the first intelligent universal system that yields double results with half the effort for engineering a DNA CLPs library and various DNA combinatorial logic circuits. Differing from previous DNA logic systems, as for the non-interference between two substrates, “Pos^Neg” gates of each DNA CLPs in this system were operated via the same DNA reaction at one time, without gates’ redesign/reoperation. With the modulation of DNA reactions, a DNA CLPs library was fabricated. Moreover, through switching the selective/parallel operating-mode, “Pos^Neg” gates of each CLP could not only be alternatively constructed, but also be integrated into DNA combinatorial logic circuits (Pos/p/Neg). All the strategies largely simplified the operation and reduced the time/costs of current DNA gates’ construction by at least 1/2, accompanied with significantly improved computing efficiency. Furthermore, a DNA voter with “One-vote Deny” function that executed by multiple equal deniers was realized.

Chemiluminescence of CsPbBr3 Perovskite Nanocrystal on the Hexane/Water Interface

All-inorganic halide perovskite CsPbBr3 nanocrystals (NCs) have attracted more attention in recent years due to the unique optical feature. To date, most of the research was mainly focused on the photoluminescence (PL) and electrochemiluminescence (ECL) of the perovskite NCs. In this work, the strong chemiluminescence (CL) emission of CsPbBr3 NCs was observed for the first time on the hexane/water interface with the assistance of ammonium persulfate-(NH4)2S2O8 as coreactant. Different coreactants were investigated to demonstrate the effect on the CL behavior and it was found that CL intensity achieved the maximum in the presence of (NH4)2S2O8. In this system, electron transfer took place on the surface of the CsPbBr3 NCs, and the excited CsPbBr3 NCs was originated from the direct chemical oxidation of (NH4)2S2O8. The CL spectrum of CsPbBr3 NCs was also collected and was consistent with their PL and ECL spectra, indicating that CsPbBr3 NCs played a role of luminophor during the CL process. The discovery of monochromatic CL of highly crystallized CsPbBr3 NCs not only extends the applications of halide perovskite materials in the analytical field but also provides a new route for the exploration of the physical chemistry properties.