Near infrared sensing based on fluorescence resonance energy transfer between Mn:CdTe quantum dots and Au nanorods

Rapid recognition of di-n-butyl phthalate in food samples with a near infrared fluorescence imprinted sensor based on zeolite imidazolate framework-67

Di-n-butyl phthalate (DBP) as a plasticizer is widely used in food and chemical industries. It is harm to human health when it appeared in food and water. A novel near-infrared (NIR) fluorescence molecularly imprinted sensor based on CdTe quantum dots and zeolite imidazolate framework-67 was developed with a sol-gel polymerization method for rapid and sensitive determination of DBP in foodstuff rapidly (only in 1.5 min). The fluorescence imprinted sensor provided a rapid detection method for DBP in the linear response concentration range of 0.05-18.0 μM with a low detection limit of 1.6 nM. Compared with previous fluorescence imprinted sensor, it behaved faster response speed and lower detection limit for determination of DBP. The fluorescence imprinted sensor was used to detect DBP in real samples successfully with satisfied recoveries of 97.2-106.4%, suggesting a potential application in food analysis.

Gold nanorods-mediated efficient synergistic immunotherapy for detection and inhibition of postoperative tumor recurrence

Tumor recurrence after surgery is the main cause of treatment failure. However, the initial stage of recurrence is not easy to detect, and it is difficult to cure in the late stage. In order to improve the life quality of postoperative patients, an efficient synergistic immunotherapy was developed to achieve early diagnosis and treatment of post-surgical tumor recurrence, simultaneously. In this paper, two kinds of theranostic agents based on gold nanorods (AuNRs) platform were prepared. AuNRs and quantum dots (QDs) in one agent was used for the detection of carcinoembryonic antigen (CEA), using fluorescence resonance energy transfer (FRET) technology to indicate the occurrence of in situ recurrence, while AuNRs in the other agent was used for photothermal therapy (PTT), together with anti-PDL1 mediated immunotherapy to alleviate the process of tumor metastasis. A series of assays indicated that this synergistic immunotherapy could induce tumor cell death and the increased generation of CD3⁺/CD4⁺ T-lymphocytes and CD3⁺/CD8⁺ T-lymphocytes. Besides, more immune factors (IL-2, IL-6, and IFN-γ) produced by synergistic immunotherapy were secreted than mono-immunotherapy. This cooperative immunotherapy strategy could be utilized for diagnosis and treatment of postoperative tumor recurrence at the same time, providing a new perspective for basic and clinical research.

The study of chiral recognition on ibuprofen enantiomers by a fluorescent probe based on β-cyclodextrin modified ZnS:Mn quantum dots

In this paper, a fluorescence method for chiral detection of ibuprofen and its enantiomer was developed. The L-cystenine-capped ZnS:Mn quantum dots were synthesized and functionalized with β-cyclodextrin (β-CD-QDs). The β-CD-QDs exhibited different quenching effect to the S-(+)-ibuprofen and the R-(-)-ibuprofen based on the advantage of the inclusion complex of cyclodextrin. It was found that the quenching of β-CD-QDs by S-(+)-ibuprofen was due to the formation of inclusion complex through both static quenching and photoinduced electron transfer, but only slight quenching with the R-(-)-ibuprofen. The stability constants derived from Hildebrand-Benesi method and absorption titration experiments were applied to determine the stability constants of the formed complexes, the double reciprocal plots suggest that a conclusion complex with a ratio of 1:1 was formed between β-CD-QDs and S-(+)-ibuprofen, but did not with the R-(-)-ibuprofen. The fluorescence intensity of the β-CD-QDs was linearly dependent on the concentration of the S-(+)-IBP in the range of 0-0.5 nmol/L with an limit of detection of 0.29 nmol/L.

Research Progress of Near-Infrared Fluorescence Immunoassay

Near-infrared fluorescence probes (NIFPs) have been widely used in immunoassay, bio-imaging and medical diagnosis. We review the basic principles of near-infrared fluorescence and near-infrared detection technology, and summarize structures, properties and characteristics of NIFPs (i.e., cyanines, xanthenes fluorescent dyes, phthalocyanines, porphyrin derivates, single-walled carbon nanotubes (SWCNTs), quantum dots and rare earth compounds). We next analyze applications of NIFPs in immunoassays, and prospect the application potential of lateral flow assay (LFA) in rapid detection of pathogens. At present, our team intends to establish a new platform that has highly sensitive NIFPs combined with portable and simple immunochromatographic test strips (ICTSs) for rapid detection of food-borne viruses. This will provide technical support for rapid detection on the port.

Optical demodulation system for digitally encoded suspension array in fluoroimmunoassay

A laser-induced breakdown spectroscopy and fluorescence spectroscopy-coupled optical system is reported to demodulate digitally encoded suspension array in fluoroimmunoassay. It takes advantage of the plasma emissions of assembled elemental materials to digitally decode the suspension array, providing a more stable and accurate recognition to target biomolecules. By separating the decoding procedure of suspension array and adsorption quantity calculation of biomolecules into two independent channels, the cross talk between decoding and label signals in traditional methods had been successfully avoided, which promoted the accuracy of both processes and realized more sensitive quantitative detection of target biomolecules. We carried a multiplexed detection of several types of anti-IgG to verify the quantitative analysis performance of the system. A limit of detection of 1.48×10-10  M was achieved, demonstrating the detection sensitivity of the optical demodulation system.

Highly Sensitive Homogeneous Immunoassays Based on Construction of Silver Triangular Nanoplates-Quantum Dots FRET System

With growing concerns about health issues worldwide, elegant sensors with high sensitivity and specificity for virus/antigens (Ag) detection are urgent to be developed. Homogeneous immunoassays (HIA) are an important technique with the advantages of small sample volumes requirement and pretreatment-free process. HIA are becoming more favorable for the medical diagnosis and disease surveillance than heterogeneous immunoassays. An important subset of HIA relies on the effect of fluorescence resonance energy transfer (FRET) via a donor-acceptor (D-A) platform, e.g., quantum dots (QDs) donor based FRET system. Being an excellent plasmonic material, silver triangular nanoplates (STNPs) have unique advantages in displaying surface plasmon resonance in the visible to near infrared spectral region, which make them a better acceptor for pairing with QDs in a FRET-based sensing system. However, the reported STNPs generally exhibited broad size distributions, which would greatly restrict their application as HIA acceptor for high detection sensitivity and specificity purpose. In this work, uniform STNPs and red-emitting QDs are firstly applied to construct FRET nanoplatform in the advanced HIA and further be exploited for analyzing virus Ag. The uniform STNPs/QDs nanoplatform based medical sensor provides a straightforward and highly sensitive method for Ag analysis in homogeneous form.

Chemical sensing with nanoparticles as optical reporters: from noble metal nanoparticles to quantum dots and upconverting nanoparticles

A wide variety of biological and medical analyses are based on the use of optical signals to report specific molecular events. Thanks to advances in nanotechnology, various nanostructures have been extensively used as optical reporters in bio- and chemical assays. This review describes recent progress in chemical sensing using noble metal nanoparticles (gold and silver), quantum dots and upconverting nanoparticles. It provides insights into various nanoparticle-based sensing strategies including fluorescence/luminescence resonance energy transfer nanoprobes as well as activatable probes sensitive to specific changes in the biological environment. Finally we list some research challenges to be overcome in order to accelerate the development of applications of nanoparticle bio- and chemical sensors.

Turn-on fluorescent sensing of glutathione S-transferase at near-infrared region based on FRET between gold nanoclusters and gold nanorods

A fluorescence resonance energy transfer (FRET) method based on gold nanoclusters capped glutathione (AuNCs@GSH) and amine-terminated gold nanorods (AuNRs) is designed for turn-on and near-infrared region (NIR) sensing of glutathione S-transferase (GST). The absorption band of AuNRs is tuned carefully to maximize the spectra overlap and enhance the efficiency of FRET. The FRET from multiple AuNCs to single AuNR quenches about 70% fluorescence emission of AuNCs. After GST is added, the strong specific interaction of GSH-GST can replace the AuNCs@GSH from AuNRs, FRET based on electrostatic interaction between AuNCs@GSH and AuNRs is switched off. Thus, emission enhancement of AuNCs@GSH is observed. The fluorescent enhancement is linearly with the increasing GST concentration over the range of 2-100 nM GST and the limit of detection for GST is about 1.5 nM.

Multiplexed DNA detection using a gold nanorod-based fluorescence resonance energy transfer technique

A fluorescence resonance energy transfer method for multiplex detection DNA based on gold nanorods had been successfully constructed. This method is simple, easy to operate, good selectivity, no requirement to label the probe molecule and can analyze simultaneously multiple targets of DNA in one sample. The limit of detection for the 18-mer, 27-mer and 30-mer targets is 0.72, 1.0 and 0.43 nM at a signal-to-noise ratio of 3. The recoveries of three targets were 96.57-98.07%, 99.12-100.04% and 97.29-99.93%, respectively. The results show that the method can be used to analyze a clinical sample or a biological sample; it also can be used to develop new probes for rapid, sensitive and highly selective multiplex detection of analytes in real samples.

A sensitive quenched electrochemiluminescent DNA sensor based on the catalytic activity of gold nanoparticle functionalized MoS2

A simple sandwich-type ECL sensor for DNA detection based on MoS₂–Au quenching the ECL signal of CdS/ZnS QDs.

A FRET-based carbon dot–MnO2nanosheet architecture for glutathione sensing in human whole blood samples

A novel FRET model employing fluorescent carbon dots and MnO₂nanosheets as donor–acceptor pairs is built for GSH sensing.

A near infrared fluorescence resonance energy transfer based aptamer biosensor for insulin detection in human plasma

A new FRET model using near-infrared quantum-dots (NIR-QDs) and oxidized carbon nanoparticles (OCNPs) as the energy donor and acceptor was constructed and designed for insulin detection in complex human plasma.

Quantum dots based molecular beacons for in vitro and in vivo detection of MMP-2 on tumor

Matrix metalloproteinase-2 (MMP-2) is a protease related to tumor invasion and metastasis. It is heavily secreted by malignant tumor cells, allowing the protease to serve as an imaging biomarker of cancer. In this study, a novel sensing system based on fluorescence resonance energy transfer (FRET) from quantum dot (QD, the donor) to organic dye (the acceptor) was constructed for the in vitro and in vivo detection of matrix metalloproteinases-2 via a MMP-2-specific peptide substrate (GPLGVRGKGG). Specifically, 535 nm-emitting CdTe QD were bound to Rhodamine B (RB) through the peptide for in vitro detection of MMP-2, while 720 nm-emitting CdTeS QDs was linked to near infrared dye ICG-Der-02 (MPA) by the peptide for measurement in vivo. When these probes were exposed to MMP-2, the selective cleavage of the peptide resulted in the recovery of fluorescence from QDs. By using the produced 540QD-peptide-RB and 720QD-peptide-MPA probes, we successfully examined MMP-2 in live cells and tumor on nude mouse, respectively. Due to the tunable fluorescence of Qds, this nanosensor can be fine-tuned for a wide range of applications such as the detection of different biomarkers and early diagnosis of disease.

Nonexclusive fluorescent sensing for L/D enantiomers enabled by dynamic nanoparticle-nanorod assemblies

Fluorescence sensing of enantiomers is a much needed yet very challenging task due to nearly identical chemical and physical properties of the chiral isomers also known as chiral equivalence. In this study, we propose a novel strategy for fluorescence sensing of enantiomers using chiral nanoparticles and their ability to form dynamic assemblies. Fluorescence resonance energy transfer (FRET) in nanoscale assemblies consisting of either L-cysteine- or D-cysteine-modified quantum dots (QDs) and gold nanorods (GNRs) was found to be strongly dependent on traces of cysteine. This occurs due to high sensitivity of dynamic assemblies to the weak internanoparticle interactions that can exponentially increase energy transfer efficiencies from QDs to GNRs. Comprehensive analysis of the fluorescence responses in the two types of chiral nanoscale assemblies enables accurate determination of both concentration and enantiomeric composition of the analyte, i.e., cysteine. The described method can quantify the composition of a chiral sample, even the content of one enantiomer is as low as 10% in the mixture. Exceptional selectivity in respect to D/L-cysteine in comparison to analogous small molecules was observed. Versatility of nanoparticle-nanorod assemblies and tunability of intermolecular interactions in them open the road to adaptation of this sensing platform to other chiral analytes.

Homogeneous fluorescence-based immunoassay via inner filter effect of gold nanoparticles on fluorescence of CdTe quantum dots

Homogeneous immunoassays are becoming more and more attractive for modern medical diagnosis because they are superior to heterogeneous immunoassays in sample and reagent consumption, analysis time, portability and disposability. Herein, a universal platform for homogeneous immunoassay, using human immunoglobulin (IgG) as a model analyte, has been developed. This assay relies upon the inner filter effect (IFE) of gold nanoparticles (AuNPs) on CdTe QDs fluorescence. The immunoreaction of antigen and antibody can induce the aggregation of antibody-functionalized AuNPs, and after aggregation the IFE of AuNPs on CdTe QDs fluorescence is greatly enhanced, resulting in a decrease of fluorescence intensity in the system. Based on this phenomenon, a wide dynamic range of 1-100 pg mL(-1) for determination of IgG can be obtained. The proposed method shows a detection limit of 0.3 pg mL(-1) for human IgG, which is much lower than the corresponding absorbance-based approach and compares favorably with other reported fluorescent methods. This immunoassay method is simple, rapid, cheap, and sensitive. The proposed method has been successfully applied to measuring IgG in serum samples, and the obtained results agreed well with those of the enzyme-linked immunosorbent assay (ELISA).

Exploiting the light–metal interaction for biomolecular sensing and imaging

The ability of metal surfaces and nanostructures to localize and enhance optical fields is the primary reason for their application in biosensing and imaging. Local field enhancement boosts the signal-to-noise ratio in measurements and provides the possibility of imaging with resolutions significantly better than the diffraction limit. In fluorescence imaging, local field enhancement leads to improved brightness of molecular emission and to higher detection sensitivity and better discrimination. We review the principles of plasmonic fluorescence enhancement and discuss applications ranging from biosensing to bioimaging.

Intermolecular and intramolecular quencher based quantum dot nanoprobes for multiplexed detection of endonuclease activity and inhibition

DNA cleavage by endonucleases plays an important role in many biological events such as DNA replication, recombination, and repair and is used as a powerful tool in medicinal chemistry. However, conventional methods for assaying endonuclease activity and inhibition by gel electrophoresis and chromatography techniques are time-consuming, laborious, not sensitive, or costly. Herein, we combine the high specificity of DNA cleavage reactions with the benefits of quantum dots (QDs) and ultrahigh quenching abilities of inter- and intramolecular quenchers to develop highly sensitive and specific nanoprobes for multiplexed detection of endonucleases. The nanoprobe was prepared by conjugating two sets of DNA substrates carrying quenchers onto the surface of aminated QDs through direct assembly and DNA hybridization. With this new design, the background fluorescence was significantly suppressed by introducing inter- and intramolecular quenchers. When these nanoprobes are exposed to the targeted endonucleases, specific DNA cleavages occur and pieces of DNA fragments are released from the QD surface along with the quenchers, resulting in fluorescence recovery. The endonuclease activity was quantified by monitoring the change in the fluorescence intensity. The detection was accomplished with a single excitation light. Multiplexed detection was demonstrated by simultaneously assaying EcoRI and BamHI (as model analytes) using two different emissions of QDs. The limits of detection were 4.0 × 10(-4) U/mL for EcoRI and 8.0 × 10(-4) U/mL for BamHI, which were at least 100 times more sensitive than traditional gel electrophoresis and chromatography assays. Moreover, the potential application of the proposed method for screening endonuclease inhibitors has also been demonstrated. The assay protocol presented here proved to be simple, sensitive, effective, and easy to carry out.

Gold nanorods-based FRET assay for ultrasensitive detection of Hg2+

A fluorescence method for detecting mercury ion in a homogeneous medium is proposed with gold nanorods (GNRs) as a fluorescence quencher on the basis of the fluorescence resonance energy transfer (FRET). Under the optimum conditions, the method exhibits a dynamic response range from 10 pM to 5 nM with a detection limit of 2.4 pM.

Electrochemiluminescence based on quantum dots and their analytical application

This review presents a general description of the electrochemiluminescence (ECL) related to quantum dots (QDs) and their analytical application. It briefly overviews the synthetic route of quantum dots. The basic mechanisms are given for QDs ECL behavior. Finally, new developments and improvements of its application in inorganic substance analysis, organics analysis, immunoassay and aptasensing assay are discussed.