Magnetic Bead Spherical Nucleic Acid Microstructure for Reliable DNA Preservation and Repeated DNA Reading.

DNA is an attractive medium for long-term data storage because of its density, ease of copying, sustainability, and longevity. Recent advances have focused on the development of new encoding algorithms, automation, and sequencing technologies. Despite progress in these subareas, the most challenging hurdle in the deployment of DNA storage remains the reliability of preservation and the repeatability of reading. Herein, we report the construction of a magnetic bead spherical nucleic acid (MB-SNA) composite microstructure and its use as a cost-effective platform for reliable DNA preservation and repeated reading. MB-SNA has an inner core of silica@γ-Fe2O3@silica microbeads and an outer spherical shell of double-stranded DNA (dsDNA) with a density as high as 34 pmol/cm2. For MB-SNA, each strand of dsDNA stored a piece of data, and the high-density packing of dsDNA achieved high-capacity storage. MB-SNA was advantageous in terms of reliable preservation over free DNA. By accelerated aging tests, the data of MB-SNA is demonstrated to be readable after 0.23 million years of preservation at -18 °C and 50% relative humidity. Moreover, MB-SNA facilitated repeated reading by facile PCR-magnetic separation. After 10 cycles of PCR access, the retention rate of dsDNA for MB-SNA is demonstrated to be as high as 93%, and the accuracy of sequencing is more than 98%. In addition, MB-SNA makes cost-effective DNA storage feasible. By serial dilution, the physical limit for MB-SNA to achieve accurate reading is probed to be as low as two microstructures.

An optical keypad lock with high resettability based on a quantum dot-porphyrin FRET nanodevice.

Due to their appealing properties, nanomaterials have become ideal candidates for the implementation of computing systems. Herein, an optical keypad lock based on a Förster resonance energy transfer (FRET) nanodevice is developed. The nanodevice is composed of a green-emission quantum dot with a thick silica shell (gQD@SiO2) and peripheric blue-emission quantum dots with ultrathin silica spacer (bQD@SiO2), on which 5,10,15,20-tetrakis(4-sulfophenyl)porphyrin (TSPP) is covalently linked. The nanodevice outputs dual emission-based ratiometric fluorescence, depending on the FRET efficiency of bQD-porphyrin pairs, which is highly sensitive to the metalation of TSPP: values are 59.7%, 44.8%, and 10.1% for bQD-Zn(ii)TSPP, bQD-TSPP, and bQD-Fe(iii)TSPP pairs, respectively. As such, by using the competitive chelation-induced transmetalation of TSPP, the nanodevice is capable of implementing a 3-input keypad lock that is unlocked only by the correct input order of Zn(ii) chelator, iron ions, and UV light. Interestingly, the reversible transmetalation of TSPP permits the reset (lock) operation of the keypad lock with the correct input order of ascorbic acid, Zn(ii), and UV light. Application of the nanodevice is exemplified by the construction of paper and cellular keypad locks, respectively, both of which feature signal readability and/or high resettability, showing high potential for personal information identification and bio-encryption applications.

Liposomal Spherical Nucleic Acid Scaffolded Site-Selective Hybridization of Nanoparticles for Visual Detection of MicroRNAs.

In this study, the advanced liposomal spherical nucleic acid (L-SNA) is exploited for the first time to establish a spherical, three-dimensional biosensing platform by hybridizing with a set of nanoparticles. By hydrophilic and hydrophobic interactions as well as programmable base-pairing, red-emission quantum dots (QDs), green-emission QDs, and gold nanoparticles (AuNPs) are encapsulated into the internal aqueous core, the intermediate lipid bilayer, and the outer SNA shell, respectively, producing an L-SNA-nanoparticle hybrid. As a result of the site-selective encapsulation, the hybrid constitutes a liposomal fluorescent "core-resonance energy transfer" system surrounded by a SNA shell, as is imaged at the single-particle resolution by confocal microscopy. With the outer SNA shell as three-dimensional substrate for duplex-specific nuclease target recycling reaction, the hybrid is capable of amplified detection of microRNAs, featuring one target to many AuNP-manipulated, dual-emission QD-based ratiometric fluorescence. More importantly, the ratiometric fluorescence facilitates the hybrid to visualize microRNAs with remarkably high resolution, which is exemplified by traffic light-type transition in fluorescence color for diagnosing circulating microRNAs in clinical serum samples. Substantially, the controllable hybridization with functional nanoparticles opens an avenue for the exciting biomedical applications of liposomal spherical nucleic acids.

Quantum Dot Based Fluorescent Traffic Light Nanoprobe for Specific Imaging of Avidin-Type Biotin Receptor and Differentiation of Cancer Cells.

Sensitive and specific visualization of cell surface biotin receptors (BRs) a class of clinically important biomarkers, remains a challenge. In this work, a dual-emission ratiometric fluorescent nanoprobe is developed for specific imaging of cell surface avidin, a subtype of BRs. The nanoprobe comprises a dual-emission quantum dot nanohybrid, wherein a silica-encapsulated red-emitting QD (rQD@SiO2) is used as the "core" and green-emitting QDs (gQDs) are used as "satellites", which are further decorated with a new "love-hate"-type BR ligand, a phenanthroline-biotin conjugate with an amino linker. The nanoprobe shows intense rQD emission but quenched gQD emission by the BR ligand. Upon imaging, the rQD emission stays constant and the gQD emission is restored as cell surface avidin accrues. Accordingly, the overlaid fluorescence color collected from red and green emission changes from red to yellow and then to green. We refer to such a color change as a traffic light pattern and the nanoprobe as a fluorescent traffic light nanoprobe. We demonstrate the application of our fluorescent traffic light nanoprobe to characterize cancer cells. By the traffic light pattern, cervical carcinoma and normal cells, as well as different-type cancer cells including BR-negative colon cancer cells, BR-positive hepatoma carcinoma cells, breast cancer cells, and their subtypes, have been visually differentiated. We further demonstrate a use of our nanoprobe to distinguish the G2 phase from other stages in a cell cycle. These applications provide new insights into visualizing cell surface biomarkers with remarkable imaging resolution and accuracy.

Deciphering optimal biostimulation strategy of supplementing anthocyanin-abundant plant extracts for bioelectricity extraction in microbial fuel cells.

BACKGROUND: Microbial fuel cells (MFCs) are effective biofuel devices that use indigenous microbes to directly convert chemical energy from organics oxidation into bioelectric energy. To maximize energy-converting efficiency for bioelectricity generation in MFCs, redox mediators (RMs) (e.g., extracts obtained from plant resource-Camellia green tea) have been explored for optimal stimulation upon electron transfer (ET) capabilities. Anthocyanins are natural antioxidants widely used in food science and medicinal industry. This first-attempt study revealed optimal strategies to augment extracts of anthocyanin-rich herbs (Lycium ruthenicum Murr., Clitoria ternatea Linn. and Vaccinium Spp.) as biofuel sources of catalytic RMs for stimulating bioenergy extraction in MFCs. RESULTS: This work showed that extracts of anthocyanin-rich herbs were promising electroactive RMs. The maximal power density of MFCs supplemented with extract of L. ruthenicum Murr. was achieved, suggesting that extract of L. ruthenicum Murr. would be the most electrochemically appropriate RMs. Compared to C. ternatea Linn. and Vaccinium Spp., L. ruthenicum Murr. evidently owned the most significant redox-mediating capability to stimulate bioenergy extraction likely due to significantly high contents of polyphenols (e.g., anthocyanin). Evidently, increases in adenosine triphosphate (ATP) content directly responded to supplementation of anthocyanin-rich herbal extracts. It strongly suggested that the electron-shuttling characteristics of RMs upon electroactive microorganisms could effectively promote the electron transfer capability to maximize bioenergy extraction in MFCs. CONCLUSION: Anthocyanin as the main water-soluble vacuolar pigments in plant products were very electroactive for not only excellent antioxidant activities, but also promising electron-shuttling capabilities for renewable biofuel applications. This work also suggested the electron-shuttling mechanism of RMs that could possibly promote electron transport phenomena through microbial cell membrane, further influencing the electron transport chain for efficient bioenergy generation.

Exploring the glyphosate-degrading characteristics of a newly isolated, highly adapted indigenous bacterial strain, Providencia rettgeri GDB 1.

This study explored the characteristics of a newly isolated glyphosate (GLYP)-degrading bacterium Providencia rettgeri GDB 1, for GLYP bioremediation. Due to the serial selection pressure of high GLYP concentrations for enriched isolation, this highly tolerant GLYP biodegrader shows very promising capabilities for GLYP removal (approximately 71.4% degradation efficiency) compared to previously reported strains. High performance liquid chromatography analyses showed aminomethylphosphonic acid (AMPA) rather than sarcosine (SAR) to be the sole intermediate of GLYP decomposition via the AMPA formation pathway. Moreover, GLYP biodegradation was biochemically favorable in aerobic cultures due to its strong growth-associated characteristics. To the best of our knowledge, this is the first report to indicate that bacterial strains in the Providencia genus could demonstrate highly promising GLYP-degrading characteristics in environments with high GLYP contents.

Ligation-Rolling Circle Amplification on Quantum Dot-Encoded Microbeads for Detection of Multiplex G-Quadruplex-Forming Sequences.

The combination of microbead array with assay chemistry of isothermal amplification enables the continuous development of nucleic acid detection techniques. Herein we report the implementation of ligation-rolling circle amplification (RCA) reaction on quantum dots-encoded microbead (Qbead) for the detection of multiplex G-quadruplex (G4) forming sequences. The reaction time of RCA on the Qbead was optimized to be 60 min. Zinc phthalocyanine (ZnPc), a molecular "light switch", was selected as the G4-specific label. In the presence of target, the target-triggered ligation-RCA produced long DNA concatemer consisting of tandem repeats of G4-forming sequence, and the labeling helped generate G4/ZnPc nanowires on the Qbead. With the G4/ZnPc nanowires as fluorescent labels, the array of three encoded Qbeads was capable of detecting three G4-forming sequences by flow cytometry in a high-throughput and specific manner. Alternatively, with the G4/ZnPc nanowires as catalytic labels, chemiluminescence of H2O2-mediated oxidation of luminol could be used for detecting the target G4-forming sequences with high sensitivity. The catalytic chemiluminescence achieved a limit of detection of 0.5 ng of genomic DNA with 5 logs of linear dynamic range for the detection of the blood sample of a myeloproliferative neoplasms patient. Together the proposed isothermal amplification-on-Qbead assay featured robust detection platform, significant signal amplification, and flexible detection strategy, holding high potential in application in large-scale or "focused" nucleic acid testing.

Supramolecularly Assembled Ratiometric Fluorescent Sensory Nanosystem for "Traffic Light"-Type Lead Ion or pH Sensing.

The combination of functional nucleic acids and nanomaterials enables the continuous development of hybrid nanosystems that have found wide applications including chemo/biosensing. Herein, we report the supramolecular assembly of a "sesame biscuit"-like superstructural nanosystem based on aptamer, quantum dot (QD), and graphene oxide (GO), and its diverse applications in Pb2+ and pH sensing. The nanosystem was assembled via adsorbing silica-encapsulated green-emitting QD onto the edge of GO by ionic interaction, followed by absorbing aptamer-modified red-emitting QD onto the GO surface via the π-stacking interaction. The nanosystem showed the characteristic of the nonquenched green fluorescence due to silica encapsulation and quenched red fluorescence owing to nanomaterial surface energy transfer. The nanosystem responded to Pb2+/pH in ratiometric fluorescence: the red fluorescence varied upon analyte-driven conformational changes of the aptamer, whereas the green one remained constant. Under optimized conditions, the nanosystem was demonstrated to be capable of quantifying Pb2+ with a detection limit of 11.7 pM, as well as pH with a sensing resolution of 0.1 pH unit. More importantly, the ratiometric nanosystem facilitated visualization of analytes in a distinct "traffic light" manner, which was exemplified by semiquantification of exogenous Pb2+ in living cells. To demonstrate practicality, fluorescent test strips were fabricated by immobilizing the nanosystem on paper. The fluorescent test strips displayed traffic light-type fluorescence color changes, with the capacity for on-site, naked-eye detection of Pb2+ in real samples, as well as point-of-care pH testing in routine urinalysis.

Deciphering synergistic characteristics of redox mediators-stimulated echinenone production of Gordonia terrae TWIH01.

This first-attempt study tended to decipher synergistic interactions of model redox mediators (RMs) to echinenone production for electrochemically-steered fermentation (ESF). The findings indicated that supplement of RMs could significantly stimulate the production performance of fermentation (e.g., 36% for 4-aminophenol) which was parallel with stimulation of bioelectricity generation in microbial fuel cells (MFCs) as prior studies mentioned. Although redox mediators could usually enhance electron transport extracellular compartment, the mechanisms of bioelectricity generation in MFCs and echinenone production in ESF were very likely functioned in the extracellular and the intracellular compartment, respectively. In MFCs, electron transfer towards biofilm anode for bioelectricity generation must be taken place. However, for ESF echinenone accumulation was very likely occurred in the intracellular compartment, thus electron transfer was predominantly implemented in the intracellular, not the extracellular compartment.

Strand Displacement Amplification Reaction on Quantum Dot-Encoded Silica Bead for Visual Detection of Multiplex MicroRNAs.

The combination of microbead array, isothermal amplification, and molecular signaling enables the continuous development of next-generation molecular diagnostic techniques. Herein we reported the implementation of nicking endonuclease-assisted strand displacement amplification reaction on quantum dots-encoded microbead (Qbead), and demonstrated its feasibility for multiplexed miRNA assay in real sample. The Qbead featured with well-defined core-shell superstructure with dual-colored quantum dots loaded in silica core and shell, respectively, exhibiting remarkably high optical encoding stability. Specially designed stem-loop-structured probes were immobilized onto the Qbead for specific target recognition and amplification. In the presence of low abundance of miRNA target, the target triggered exponential amplification, producing a large quantity of stem-G-quadruplexes, which could be selectively signaled by a fluorescent G-quadruplex intercalator. In one-step operation, the Qbead-based isothermal amplification and signaling generated emissive "core-shell-satellite" superstructure, changing the Qbead emission-color. The target abundance-dependent emission-color changes of the Qbead allowed direct, visual detection of specific miRNA target. This visualization method achieved limit of detection at the subfemtomolar level with a linear dynamic range of 4.5 logs, and point-mutation discrimination capability for precise miRNA analyses. The array of three encoded Qbeads could simultaneously quantify three miRNA biomarkers in ∼500 human hepatoma carcinoma cells. With the advancements in ease of operation, multiplexing, and visualization capabilities, the isothermal amplification-on-Qbead assay could potentially enable the development of point-of-care diagnostics.

A quantum dot-labelled aptamer/graphene oxide system for the construction of a half-adder and half-subtractor with high resettability.

By a combination of quantum dot-labelled aptamers and graphene oxide, a hybrid molecular system was developed for the integration of multiple logic gates to implement half adder and half subtractor functions. On the merits of quantum dots, repetitious arithmetic operations and a reliable fluorescent switch were demonstrated.

Hybridization chain reactions on silica coated Qbeads for the colorimetric detection of multiplex microRNAs.

A robust Qbead platform that integrated with target-binding, hybridization chain reaction and staining was developed for the direct multiplexed detection of endogenous miRNAs by amplified Qbead-colour change.

QD-Biopolymer-TSPP Assembly as Efficient BiFRET Sensor for Ratiometric and Visual Detection of Zinc Ion.

In this work, we report a new type of quantum dot (QD)-based fluorescence resonance energy transfer (FRET) assembly and its utility for sensing Zn2+ in different media. The assembly on the QD scaffold is via first coating of poly(dA) homopolymer/double-stranded DNA, followed by loading of meso-tetra(4-sulfonatophenyl)porphine dihydrochloride (TSPP), both of which are electrostatic, offering the advantages of cost-efficiency and simplicity. More importantly, the biopolymer coating minimizes the interfacial thickness to be ≤2 nm for QD-TSPP FRET, which results in improvements of up to 60-fold for single FRET efficiency and nearly 4-fold for total FRET efficiency of the QD-biopolymer-TSPP assemblies in comparison with silica-coating-based QD-TSPP assemblies. On the basis of Zn2+-chelation-induced spectral modulation, dual-emission QD-poly(dA)-TSPP assemblies are developed as a ratiometric Zn2+ sensor with increased sensitivity and specificity. The sensor either in solution or on a paper substrate displays continuous color changes from yellow to bright green toward Zn2+, exhibiting excellent visualization capability. By utilizing the competitive displacement of Zn2+, the sensor is also demonstrated to have good reversibility. Furthermore, the sensor is successfully used to visualize exogenous Zn2+ in living cells. Together the QD-biopolymer-TSPP assembly provides an inexpensive, sensitive, and reliable sensing platform not only for on-site analytical applications but also for high-resolution cellular imaging.

Quantum Dots-Ligand Complex as Ratiometric Fluorescent Nanoprobe for Visual and Specific Detection of G-Quadruplex.

By complexing a nonionic G-quadruplex ligand with hybrid dual-emission quantum dots (QDs), a ratiometric fluorescent nanoprobe is developed for G-quadruplex detection in a sensitive and specific manner. The QDs nanohybrid comprised of a green-emission QD (gQD) and multiple red-emission QDs (rQDs) inside and outside of a silica shell, respectively, is utilized as the signal displaying unit. Only the presence of G-quadruplex can displace the ligand from QDs, breaking up the QDs-ligand complexation, and inducing the restoration of the rQDs fluorescence. Since the fluorescence of embedded gQD stays constant, variations of the dual-emission intensity ratios display continuous color changes from green to bright orange, which can be clearly observed by the naked eye. Furthermore, by utilizing competitive binding of a cationic ligand versus the nonionic ligand toward G-quadruplex, the nanoprobe is demonstrated to be applicable for assessing the affinity of a G-quadruplex-targeted anticancer drug candidate, exhibiting ratiometric fluorescence signals (reverse of that for G-quadruplex detection). By making use of the specificity of the ligand binding with G-quadruplex against a double helix, this nanoprobe is also demonstrated to be capable of sensitive detection of one-base mutation, exhibiting sequence-specific ratiometric fluorescence signals. By functionalizing with a nuclear localization peptide, the nanoprobe can be used for visualization of G-quadruplex in the nucleus of human cells.

Ratiometric Quantum Dot-Ligand System Made by Phase Transfer for Visual Detection of Double-Stranded DNA and Single-Nucleotide Polymorphism.

We have developed a proof-of-concept quantum dot-ligand (QD-L) system for visual selective detection of nucleic acids, in combination with a ratiometric fluorescence technique. This system comprises a dual-emission QDs nanohybrid formed by embedding a red-emission QD (rQD) in a silica nanoparticle and electrostatically assembling green-emission QDs (gQDs) onto the silica surface, as the signal displaying unit, and a hydrophobic compound, dipyrido[3,2-a:2',3'-c]phenazine (dppz), attached onto the gQDs surface via phase transfer, as the ligand as well as fluorescence quencher of gQDs. This system is successfully used for quantification of double-stranded DNA (dsDNA). Because of its avid binding with dppz, dsDNA can break up the QD-L system, displacing the dppz ligand from the gQDs surface and restoring the gQDs emission. Since the red emission of embedded rQDs stays constant, variations of the dual-emission intensity ratios display continuous color changes from orange to bright green, which can be clearly observed by the naked eye. More importantly, this system is advantageous in terms of specificity over a QD ionic conjugate, because the electrical neutrality of dppz excludes its nonspecific electrostatic association with dsDNA. The QD-L system also is capable of detecting single-nucleotide polymorphism, exhibiting sequence-specific ratiometric fluorescence as a QD-bioconjugate does, but possessing the obvious advantage in terms of low cost, with the avoidance of modification, labeling, and purification processes. Therefore, the QD-L system provides an extremely simple but general strategy for detecting nucleic acids in a facile, sensitive, and specific manner.

A molecular beacon microarray based on a quantum dot label for detecting single nucleotide polymorphisms.

In this work, we report the application of streptavidin-coated quantum dot (strAV-QD) in molecular beacon (MB) microarray assays by using the strAV-QD to label the immobilized MB, avoiding target labeling and meanwhile obviating the use of amplification. The MBs are stem-loop structured oligodeoxynucleotides, modified with a thiol and a biotin at two terminals of the stem. With the strAV-QD labeling an "opened" MB rather than a "closed" MB via streptavidin-biotin reaction, a sensitive and specific detection of label-free target DNA sequence is demonstrated by the MB microarray, with a signal-to-background ratio of 8. The immobilized MBs can be perfectly regenerated, allowing the reuse of the microarray. The MB microarray also is able to detect single nucleotide polymorphisms, exhibiting genotype-dependent fluorescence signals. It is demonstrated that the MB microarray can perform as a 4-to-2 encoder, compressing the genotype information into two outputs.

Fluorescence resonance energy transfer-based ratiometric fluorescent probe for detection of Zn(2+) using a dual-emission silica-coated quantum dots mixture.

In this work, we report the design and application of a new ratiometric fluorescent probe, which contains different-colored quantum dots (QDs) as dual fluorophores, ultrathin silica shell as spacer, and meso-tetra(4-sulfonatophenyl)porphine dihydrochloride (TSPP) as receptor, for Zn(2+) detection in aqueous solution and living cells. In the architecture of our designed probe, the silica shell plays the key roles in controlling the locations of QDs, TSPP, and Zn(2+), preventing the direct contact between QDs and Zn(2+) but affording fluorescence resonance energy transfer (FRET) from dual-color QDs to TSPP. In the presence of Zn(2+), the analyte-receptor reaction changes the absorption in the range of the Q-band of TSPP and accordingly the efficiencies of two independent FRET processes from the dual-colored QDs to the acceptor, respectively, leading to fluorescence enhancement of green-emission QDs whereas fluorescence quenching of yellow-emission QDs. Benefiting from the well-resolved dual emissions from different-colored QDs and the large range of emission ratios, the probe solution displays continuous color changes from yellow to green, which can be clearly observed by the naked eye. Under physiological conditions, the probe exhibits a stable response for Zn(2+) from 0.3 to 6 µM, with a detection limit of 60 nM in aqueous solutions. With respect to single-emission probes, this ratiometric probe has demonstrated to feature excellent selectivity for Zn(2+) over other physiologically important cations such as Fe(3+) and Cu(2+). It has been preliminarily used for ratiometric imaging of Zn(2+) in living cells with satisfying resolution.

Ligand displacement-induced fluorescence switch of quantum dots for ultrasensitive detection of cadmium ions.

This paper reports the construction of a simple CdTe quantum dots (QDs)-based sensor with 1,10-phenanthroline (Phen) as ligand, and the demonstration of a novel ligand displacement-induced fluorescence switch strategy for sensitive and selective detection of Cd(2+) in aqueous phase. The complexation of Phen at the surface quenches the green photoluminescence (PL) of QDs dominated by a photoinduced hole transfer (PHT) mechanism. In the presence of Cd(2+), the Phen ligands are readily detached from the surface of CdTe QDs, forming [Cd(Phen)2(H2O)2](2+) in solution, and as a consequence the PL of CdTe QDs switches on. The detection limit for Cd(2+) is defined as ∼0.01 nM, which is far below the maximum Cd(2+) residue limit of drinking water allowed by the U.S. Environmental Protection Agency (EPA). Two consecutive linear ranges allow a wide determination of Cd(2+) from 0.02 nM to 0.6 µM. Importantly, this CdTe QDs-based sensor features to distinctly discriminate between Cd(2+) and Zn(2+), and succeeds in real water samples. This extremely simple strategy reported here represents an attempt for the development of fluorescent sensors for ultrasensitive chemo/biodetection.

Fluorescent recognition of deoxyribonucleic acids by a quantum dot/meso-tetrakis(N-methylpyridinium-4-yl)porphyrin complex based on a photo induced electron-transfer mechanism.

We have developed a new fluorescent probe of thioglycolic acid (TGA)-capped CdTe quantum dots (QDs) complexed with a model drug, meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) for detecting deoxyribonucleic acids (DNAs). This probe operates with an "Off-On" mode: TMPyP quenches the photoluminescence (PL) of QDs via a photo induced electron-transfer (PIET) process; the presence of DNA can break the QD/TMPyP complexation, interrupting the PIET process, and switch on the PL of QDs. Sensitive detection of DNA with the detection limit of 0.16 nM and a linear detection range of 0.25-6.0 nM are achieved. Importantly, this probe can be used to distinguish the binding modes of DNA-TMPyP interactions, exhibiting the DNA sequence-dependent PL recovery behaviors. The obtained binding constant for poly(dA)·poly(dT) is ∼3.30×10(7) L mol(-1), which is approximately one order of magnitude larger than those for native DNAs and poly(dG)·poly(dC). Furthermore, the thymine bases preferential of the TMPyP-DNA interaction is proved by this probe.

Quantum dot-phenanthroline dyads: detection of double-stranded DNA using a photoinduced hole transfer mechanism.

We have developed a new fluorescent probe based on direct conjugation between 1,10-phenanthroline (Phen) and water-soluble thioglycolic acid (TGA) capped CdTe quantum dots (QDs) for the detection of double-stranded DNA (dsDNA). Phen could directly adsorb onto the QDs surface by metal-affinity driven coordination, quenching the photoluminescence (PL) of QDs via the photoinduced hole transfer process; addition of dsDNA would bring the restoration of QDs PL, as Phen could intercalate into dsDNA followed by its dissociation from the QDs surface. The dependence of QDs PL on the dsDNA amount as well as temperature was utilized to investigate the Phen-dsDNA interaction. The obtained binding constant of the QD-Phen dyad was 2-3 orders of magnitude higher than that of Phen-based metal complexes. Both the binding constant and the binding site of dsDNA with Phen increased with the elevated temperature, owing to an endothermic process. At 37 °C, sensitive detection of dsDNA with a detection limit of ~3 nmol L(-1) was achieved. Therefore, the QD-molecule direct conjugation based fluorescent probe could provide an effective alternative to those based on QD-bioconjugation and QD-ionic conjugation.