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A one-pot hydrothermal method was developed for the synthesis of graphene oxide quantum dots (GOQDs). It is making use of toner waste as the precursor and H 2 O 2 as the oxidant. Synthesis takes 4 h and does not require strong acids or complex purification steps and does not produce environmentally harmful metal ions. The GOQDs display blue fluorescence with excitation/emission maxima at 340/445 nm. The feasibility of detecting specific DNA sequence was promoted using polyethyleneimine to modify the GOQDs surface. A method was developed to recognized a specific DNA sequence. This is based on electrostatic aggregation of GOQDs and ssDNA labeled with Dabcyl at the 3' end, which promotes fluorescence quenching of GOQDs. The possible fluorescence quenching mechanism (which is mainly dynamic) was investigated using the Stern-Volmer equation. When a target sequence was added, which is complementary to the ssDNA, the dabcyl-labeled ssDNA is released due to strict complementary base pairing. This promotes fluorescence recovery of GOQDs. The assay has a 0.17 nM detection limit and a linear range of 0.5-30 nM. The method was used to quantify specific DNA sequences from extracts of genetically modified plant tissues. Graphical abstract Graphene oxide quantum dots (GOQDs) were synthesized by one-pot hydrothermal method using waste toner, and the surface was modified by polyethyleneimine (PEI). Through the interaction of PEI-GOQDs with Dabcyl-DNA single strands to dynamically quench the fluorescence of GOQDs. Based on DNA hybridization technology, we established specific DNA sequence detection nanoprobe.

A simple phosphorescence method is proposed for quercetin detection based on Al(3+)-amplified room-temperature phosphorescence (RTP) signals of 3-mercaptopropionic acid (MPA)-capped Mn-doped ZnS quantum dots (QDs). The sensor was established based on some properties as follows. Al(3+) can interact with carboxyl groups on the surface of MPA-capped Mn-doped ZnS QDs via chelation, which will lead to the aggregation of QDs and amplification of RTP signals, After the addition of quercetin, it can form more stable complex with Al(3+) in alkaline aqueous solution and dissociate Al(3+) from the surface of Mn-doped ZnS QDs, which will result in significant recovery of RTP intensity of the MPA-capped Mn-doped ZnS-Al(3+) system. Under the optimized conditions, the change of RTP intensity was proportional to the concentration of quercetin in the range from 0.1 to 6.0 mg L(-1), with a high correlation coefficient of 0.996 and a detection limit of 0.047 mg L(-1). The proposed method is potentially suitable for detection of quercetin in real samples without complicated pretreatment., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Quantum dot (QD) nanohybrids provide an effective route to explore the new properties of materials and are increasingly used as highly valuable sensitive (bio) chemical probes. Interestingly, the room-temperature phosphorescence (RTP) of 3-mercaptopropionic acid (MPA)-capped Mn-doped ZnS QDs could be remarkably enhanced by the addition of protamine. Based on the above finding, a simple, sensitive, and selective method for rapid detection of protamine was successfully designed. With this method, protamine as a cationic peptide interacts electrostatically with MPA-capped Mn-doped ZnS QDs to form MPA-capped Mn-doped ZnS QD/protamine complexes, which leads to the aggregation of QDs and enhances the RTP intensity. Under the optimized conditions, the RTP intensity change was linearly proportional to the concentration of protamine in the range 0.2-3.0 μg ml(-1), and the limit of detection was 0.14 μg ml(-1). The proposed method was successfully applied to detect protamine in protamine sulfate injection and human serum samples with satisfactory results, and the recovery ranged from 96.5 to 105.6%., (Copyright © 2015 Elsevier Inc. All rights reserved.)

A "turn off-on" switch mode was established by using the interaction between acridine orange (AO) and DNA as an input signal and using the room temperature phosphorescence (RTP) reversible change of 3-mercaptopropionic acid (MPA)-capped Mn-doped ZnS quantum dots (QDs) as an output signal in biological fluids. AO was absorbed into the surface of Mn-doped ZnS QDs via electrostatic attraction and, thus, formed a ground-state complex through photoinduced electron transfer (PIET). This complex quenched the phosphorescence of Mn-doped ZnS QDs and then rendered the system into the "turn-off" mode. Along with the addition of DNA and embedded binding with DNA, AO was competitively induced to fall off from the surface of Mn-doped ZnS QDs and embed into the double helix structure of DNA. As a result, the RTP of Mn-doped ZnS QDs was recovered and the system consequently was rendered into "turn-on" mode. In this case, a new biosensor for DNA detection was built and has a detection limit of 0.033mgL(-1) and a detection range from 0.033 to 20mgL(-1). What is more, this kind of biosensor does not require complex pretreatments and is free from the interference from autofluorescence and scattering light. Thus, this biosensor can be used to detect DNA in biological fluids., (Copyright © 2015 Elsevier Inc. All rights reserved.)

MPA-capped Mn-doped ZnS QDs/DXR nanohybrids (MPA: 3-mercaptopropionic acid; QDs: quantum dots; DXR: cetyltrimethyl ammonium bromide) were constructed via photoinduced electron transfer (PIET) and then used as a room-temperature phosphorescence (RTP) probe for detection of DNA. DXR as a quencher will quench the RTP of Mn-doped ZnS QDs via PIET, thereby forming Mn-doped ZnS QDs/DXR nanohybrids and storing RTP. With the addition of DNA, it will be inserted into DXR and thus DXR will be competitively desorbed from the surface of Mn-doped ZnS QDs, thereby releasing the RTP of Mn-doped ZnS QDs. Based on this, a new method for DNA detection was built. The sensor for DNA has a detection limit of 0.039 mg L(-1) and a linear range from 0.1 to 14 mg L(-1). The present QDs-based RTP method does not need deoxidants or other inducers as required by conventional RTP detection methods, and avoids interference from autofluorescence and the scattering light of the matrix that are encountered in spectrofluorometry. Therefore, this method can be used to detect the DNA content in body fluid., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Circulating tumor cells (CTCs) are tumor cells detached from the original lesion and getting into the blood and lymphatic circulation systems. They potentially establish new tumors in remote areas, namely, metastasis. Isolation of CTCs and following biological molecular analysis facilitate investigating cancer and coming out treatment. Since CTCs carry important information on the primary tumor, they are vital in exploring the mechanism of cancer, metastasis, and diagnosis. However, CTCs are very difficult to separate due to their extreme heterogeneity and rarity in blood. Recently, advanced technologies, such as nanosurfaces, quantum dots, and Raman spectroscopy, have been integrated with microfluidic chips. These achievements enable the next generation isolation technologies and subsequent biological analysis of CTCs. In this review, we summarize CTCs' separation with microfluidic chips based on the principle of immunomagnetic isolation of CTCs. Fundamental insights, clinical applications, and potential future directions are discussed. [ABSTRACT FROM AUTHOR]

Considering the superior optical properties of CdSe/ZnS quantum dots (QDs), specific recognition characteristics of aptamer and the strong fluorescence quenching properties of graphene oxide (GO), we constructed an aptamer-mediated composite fluorescent probe composed of aptamer-modified CdSe/ZnS QDs (QDs-IBA) and GO for specific detection of insulin. Under the mediation of aptamer, QDs-IBA were effectively adsorbed onto the GO surface, forming a stable QDs-IBA@GO complex through strong π-π stacking interactions. Consequently, the fluorescence of QDs-IBA was quenched through fluorescence resonance energy transfer (FRET) between QDs-IBA and GO. During incubation with QDs-IBA, insulin specifically bound with QDs-IBA to prevent interaction between QDs-IBA and GO, leading to the insufficient quenching of QDs-IBA fluorescence. The fluorescence intensity of QDs-IBA@GO probe was directly proportional to the amount of target insulin. Under the optimized conditions, a linear response ranging from 4.3 nM to 206.4 nM was obtained for insulin detection, and the limit of detection was 2.74 nM. The established probe demonstrated its simplicity of operation and cost-effectiveness, which was used for insulin detection in injectable insulin samples and satisfactory results were obtained. [ABSTRACT FROM AUTHOR]

A selective system was developed to detect heparin in aqueous solutions by using MPA(3-Mercaptopropionic Acid)-capped Mn-doped ZnS quantum dots (QDs)/polybrene (hexadimethrine bromide) hybrids as a sensitive room temperature phosphorescence (RTP) nanosensor. In this system, the RTP intensity of QDs was remarkably enhanced via electrostatic self-assembly after the addition of polybrene. The addition of heparin into the system was competitively bound to polybrene and enable to deprive it from the surface of QDs, as a result, the RTP intensity of Mn-doped ZnS QDs/polybrene hybrids was reduced with the increased of heparin concentration. Based on this effect, a selective system was proposed to detect heparin. Under the optimal conditions, the change of RTP intensity was proportional to the heparin concentration from 0.05 to 1.4 U mL −1 (about 0.38–10.76 μg mL −1 ) and the limit of detection (LOD) was 0.021 U mL −1 (about 0.16 μg mL −1 ). This proposed nanosensor is simple and relatively free of interference from coexisting substances, which can be applied to detect heparin in heparin injection and human serum. In addition, a new pathway was also provided based on the assembly of QDs with other cationic homopolymers for further design of biosensors and detection of biomolecules. [ABSTRACT FROM AUTHOR]

Abstract: Quantum dots (QDs) nanohybrids are an effective route to obtain new property of materials, and are very significant for developing specific materials and improving the performance of existing QDs materials. The objectives of this work are to prepare MPA-capped Mn-doped ZnS QDs/CTAB nanohybrids (MPA: 3-mercaptopropionic acid; CTAB: cetyltrimethyl ammonium bromide) through electrostatic self-assembly, to investigate the formation mechanism and the Room-Temperature Phosphorescenee (RTP) changes, and to explore the possibility of their application in detection of rutin. As a result, MPA-capped Mn-doped ZnS QDs/CTAB nanohybrids greatly improve the rutin detection ability of QDs and provide an important method for developing more convenient and effective rutin detection sensor. The sensor for rutin gave a detection limit of 0.037mgL−1 and two linear ranges from 0.05 to 0.5mgL−1 and from 0.5 to 5mgL−1, and thus can be expanded to selective detection of other substances. Since the present QDs-based RTP method does not need deoxidants or other inducers as conventional RTP detection methods, and avoids interference from autofluorescence and the scattering light of the matrix that are encountered in spectrofluorometry, this method can be used to detect the content of rutin in body fluid. [Copyright &y& Elsevier]

MPA-capped Mn-doped ZnS QDs/DXR nanohybrids (MPA: 3-mercaptopropionic acid; QDs: quantum dots; DXR: doxorubicin) were constructed via photoinduced electron transfer (PIET) and then used as a room-temperature phosphorescence (RTP) probe for the detection of DNA. DXR as a quencher will quench the RTP of Mn-doped ZnS QDs via PIET, thereby forming Mn-doped ZnS QDs/DXR nanohybrids and storing RTP. With the addition of DNA, it will be inserted into DXR and thus DXR will be competitively desorbed from the surface of Mn-doped ZnS QDs, thereby releasing the RTP of Mn-doped ZnS QDs. Based on this, a new method for DNA detection was built. The sensor for DNA has a detection limit of 0.039mgL−1 and a linear range from 0.1 to 14mgL−1. The present QDs-based RTP method does not need deoxidants or other inducers as required by the conventional RTP detection methods, and avoids interference from autofluorescence and the scattering light of the matrix that are encountered in spectrofluorometry. Therefore, this method can be used to detect the DNA content in body fluid. [ABSTRACT FROM AUTHOR]