Biosensing platform based on fluorescence resonance energy transfer from upconverting nanocrystals to graphene oxide

Hybrid MoSe2-indocyanine green nanosheets as a highly efficient phototheranostic agent for photoacoustic imaging guided photothermal cancer therapy

Phototheranostic technology based on photoacoustic imaging (PAI) and photothermal therapy (PTT) is emerging as a powerful tool for tumor theranostic applications. For effective tumor eradication, a novel PAI/PTT theranostic nanoagent with an excellent optical absorption and photothermal capability is highly desired. Herein, we present a new PAI/PTT nanohybrid named sMoSe2-ICG NSs by covalently conjugating aminated indocyanine green (ICG) onto a single layer of molybdenum selenide nanosheets (sMoSe2 NSs). We first validate the sMoSe2-ICG NS agent for the PAI and PTT effect in vitro and then use it for highly-sensitive PAI guided highly efficient tumor PTT in vivo. The sMoSe2-ICG NS hybrid possesses several advantages for PAI/PTT applications: (1) the sMoSe2-ICG NSs have strong absorbance in the broad near-infrared (NIR) region, enabling a highly efficient PAI/PTT theranostic effect and the selection of the most widely used excitation wavelength of 808 nm for PTT; (2) the photothermal ability of ICG in sMoSe2-ICG NSs is augmented due to ICG aggregation induced fluorescence quenching and the re-absorbance of ICG fluorescence by sMoSe2 NSs, which further enhances the PAI/PTT theranostic effect. (3) The characteristic absorption peak of sMoSe2-ICG NSs is red-shifted compared to free ICG, resulting in a higher PAI signal-to-noise ratio (SNR) in vivo. Thus, combined with the good stability, high biocompatibility and minimal toxicity properties, the obtained sMoSe2-ICG NSs hybrid has bright prospects for use in future PAI/PTT clinical applications.

Graphene Oxide as a Bifunctional Material toward Superior RNA Protection and Extraction

It is well known that graphene oxide (GO), a planar nanomaterial, is endowed with the capacity to immobilize short ssRNA via π-π stacking, thus enhancing its stability. However, whether large RNA molecules, such as total RNA, extracted from biological tissues can be protected using GO has not been investigated. It is usually believed that the protection of total RNA by GO is not effective because the lengths of total RNA, which range from a few to thousands of bases, are inclined to undergo desorption due to their complicated structure. Herein, the nanobiological effects of total RNA/GO are first investigated and demonstrate that the total RNA can be harbored on the surface of GO, thus resulting in a shield effect. This shield effect allows total RNA to highly resist RNase degradation and maintain RNA stability at room temperature up to 4 days, enabling the discovery of GO as the potential next-generation RNase nanoinhibitor. Furthermore, GO can be conjugated to nanomagnetic beads, defined as magnetic graphene oxide, enabling the rapid purification and protection of RNA from animal cells and tissues, whole blood, bacteria, and plant tissue.

Large-scale synthesis of uniform lanthanide-doped NaREF4 upconversion/downshifting nanoprobes for bioapplications

Lanthanide (Ln3+)-doped NaREF4 (RE = rare earth) nanocrystals (NCs) are one of the most widely studied upconversion and downshifting luminescent nanoprobes. However, the size and optical performance of the Ln3+-doped NaREF4 NCs produced by the available lab-scale synthesis may vary from batch to batch, which inevitably limits their practical bioapplications. Herein, we report the synthesis of uniform Ln3+-doped NaREF4 NCs via a facile solid-liquid-thermal-decomposition (SLTD) method by directly employing NaHF2 powder as a fluoride and sodium precursor. The proposed SLTD strategy is easy to perform, time-saving and cost-effective, making it ideal for scale-up syntheses. Particularly, over 63 g of β-NaGdF4:Yb,Er@NaYF4 core/shell NCs with narrow size variation (<7%) were synthesized via a one-pot reaction. By virtue of their superior upconversion and downshifting luminescence, we employed the synthesized core/shell nanoprobes for the in vitro detection of prostate-specific antigen with a limit of detection down to 1.8 ng mL-1, and for in vivo near-infrared imaging with a high signal-to-noise ratio of 12. These findings may pave the way for the commercialization of Ln3+-doped nanoprobes in bioassay kits for versatile clinical applications.

Fluorescent Nanobiosensors for Sensing Glucose

Glucose sensing in diabetes diagnosis and therapy is of great importance due to the prevalence of diabetes in the world. Furthermore, glucose sensing is also critical in the food and drug industries. Sensing glucose has been accomplished through various strategies, such as electrochemical or optical methods. Novel transducers made with nanomaterials that integrate fluorescent techniques have allowed for the development of advanced glucose sensors with superior sensitivity and convenience. In this review, glucose sensing by fluorescent nanobiosensor systems is discussed. Firstly, typical fluorescence emitting/interacting nanomaterials utilized in various glucose assays are discussed. Secondly, strategies for integrating fluorescent nanomaterials and biological sensing elements are reviewed and discussed. In summary, this review highlights the applicability of fluorescent nanomaterials, which makes them ideal for glucose sensing. Insight on the future direction of fluorescent nanobiosensor systems is also provided.

Controlled fluorescence quenching by antibody-conjugated graphene oxide to measure tau protein

We report an ultrasensitive immunoassay for tau protein-a key marker of Alzheimer's disease. This sensing platform relies on graphene oxide (GO) surfaces conjugated with anti-human tau antibody to provide quantitative binding sites for the tau protein. The GO quenches standard fluorescein isothiocyanate labelled tau (tau-FITC) when tau protein and tau-FITC are both present and compete for the binding sites. This change in fluorescence signal can be used to quantitate tau protein. In contrast with traditional enzyme-linked immunosorbent assay (ELISA), our method does not require enzyme-linked secondary antibodies for protein recognition nor does it require an enzyme substrate for optical signal generation. This requires fewer reagents and has less systematic error than the antigen-antibody recognition steps in ELISA. Our method has a tau protein detection limit of 0.14 pmol ml^-1 in buffer. This approach could be developed into a promising biosensor for the detection of tau protein and may be useful in the clinical diagnosis of tau-induced neurodegeneration syndromes.

Aptamer based fluorometric determination of ATP by exploiting the FRET between carbon dots and graphene oxide

The authors describe a fluorometric aptamer based assay for adenosine triphosphate (ATP). It is based on the use of carbon dots (CDs) and graphene oxide (GO). The resultant CD-aptamer is adsorbed on the surface of GO via π-stacking and hydrophobic interaction, and the fluorescence of CD-aptamer is quenched via fluorescence resonance energy transfer (FRET) between CDs and GO. If ATP is present, it will bind to the aptamer and the CD-aptamer will be desorbed from GO. This will suppress FRET and the fluorescence of the CDs is restored. Under the optimal conditions and at typical excitation/emission wavelengths of 358/455 nm, the assay has a 80 pM detection limit and a linear range that extends from 0.10 to 5.0 nM concentrations of ATP. The method was successfully applied to the determination of ATP in yogurt samples. This method can also be conceivably applied to the detection of other analytes for which appropriate aptamers are available. Graphical abstract Schematic of a novel fluorometric ATP assay based on the fluorescence resonance energy transfer (FRET) between aptamer modified carbon dots (CD-aptamer) and graphene oxide (GO). CD-aptamer was used as the energy donor and molecular recognition probe, and GO acted as energy acceptor. This assay exhibits high sensitivity and selectivity with a detection limit as low as 80 pM.

Advances in targeting the folate receptor in the treatment/imaging of cancers

The folate receptor (FR) is a recognised biomarker for tumour cells due to its overexpression on a large number of tumours. Consequently, the FR has been exploited by many diagnostic and therapeutic tools to allow targeted delivery to, and imaging of, cancer cells. Herein, we describe the many different approaches by which this has been achieved, including the attachment of folate to potent chemotherapeutic drugs to form FR-targeting small molecule-drug conjugates (SMDCs), FR-targeting antibodies (as antibody alone and as an antibody-drug conjugate), and in the form of complementary nanotechnology-folate platforms; as well as imaging variants thereof. The potential of exploiting the FR for targeted therapy/imaging has the potential to revolutionise the way several cancers are treated. These FR-targeted technologies can also pave the way for inspiring further sophisticated drug conjugates, especially as this receptor is being targeted by use of several complementary technologies: small molecule, nanoparticle and protein-based - thus providing broad and distinct knowledge in the area.

Study of Fluorescence Quenching Ability of Graphene Oxide with a Layer of Rigid and Tunable Silica Spacer

The fluorescence quenching property of graphene oxide (GO) has been newly demonstrated and applied for fluorescence imaging and biosensing. In this work, a new nanostructure was designed for effectively studying the quenching ability of GO. The key element in this design is the fabrication of a layer of rigid and thickness adjustable silica spacer for manipulating the distance between the GO and fluorophores. First, a silica core modified with organic dye molecules was prepared, followed by the formation of a silica shell with a tunable thickness. Afterward, the GO was wrapped around silica nanoparticles based on the electrostatic interaction between the negatively charged GO and positively charged silica. The quenching efficiency of GO to different dye molecules was studied at various spacer thicknesses and varying concentrations of GO. Fluorescence lifetime of fluorophores was measured to determine the quenching mechanism. We found that the quenching efficiency of GO was still around 30% when the distance between dyes and GO was increased to more than 30 nm, which indicated the long-distance quenching ability of GO and confirmed the previous theoretical calculation. The quenching mechanisms were proposed schematically based on our experimental results. We expected that the proposed nanostructure could act as a feasible model for studying GO quenching property and shed light on designing GO-based fluorescence sensing systems.

Graphite nanoparticle as nanoquencher for 17β-estradiol detection using shortened aptamer sequence

Here a shortened aptamer was used as the recognition element and a graphite nanoparticle as the nanoquencher for constructing a FRET based aptasensor to detect 17β-estradiol.

Preparation of a temperature-responsive block copolymer-anchored graphene oxide@ZnS NPs luminescent nanocomposite for selective detection of 2,4,6-trinitrotoluene

Thermo-sensitive block copolymer decorated GO@ZnS NPs nanocomposite was constructed via π–π stacking interaction as a robust fluorescent sensing platform for the selective detection of TNT.

Fluorescence immunosensor for cardiac troponin T based on Förster resonance energy transfer (FRET) between carbon dot and MoS2 nano-couple

The study demonstrates a sensitive detection technique for cardiac troponin T (cTnT) using FRET based carbon dot (CD) and molybdenum disulfide (MoS₂) nano-couple.

Temperature-sensitive poly(phenyleneethynylene) nanomedicines for intracellular tracking via fluorescence resonance energy transfer

pNIPAM-grafted poly(phenyleneethynylene) nanoparticles (pNE NPs) were synthesized by atom transfer radical polymerization and Sonogashira coupling reaction and were developed as novel self-indicating drug nano-carriers for monitoring the intracellular drug release.

Synergistically Enhanced Optical Limiting Property of Graphene Oxide Hybrid Materials Functionalized with Pt Complexes

Recently, graphene-based materials have become well-known nonlinear optical materials for the potential application of laser protection. Two new graphene oxide-platinum  complex (GO-Pt) hybrid materials (GO-Pt-1, GO-Pt-2) have been fabricated through covalent modification and electrostatic adsorption of different Pt complexes with GO. The structural and photophysical properties of the resultant hybrid materials were studied. The nonlinear optical properties and optical power limiting (OPL) performance of Pt complexes, GO, and GO-Pt hybrid materials were investigated by using Z-scan measurements at 532 nm. At the same transmittance, the results illustrate that functionalization of GO makes GO-Pt hybrid materials possess better nonlinear optical properties and OPL performance than individual Pt complexes and GO due to a combination of nonlinear scattering, nonlinear absorption, and photoinduced electron and energy transfer between GO and Pt complex moieties. Furthermore, the nonlinear optics and OPL performance of GO-Pt-2 are better than those of GO-Pt-1, due to not only the excellent optical limiting of Pt-2 and more molecules per area of GO but also the way of combination of Pt-2 and GO.

Upconversion Nanophosphor-Involved Molecularly Imprinted Fluorescent Polymers for Sensitive and Specific Recognition of Sterigmatocystin

Originated from the bottom-up synthetic strategy, molecularly imprinted polymers (MIPs) possess the inherent ability of selective and specific recognition and binding of the target analytes, with their structural cavities that can match the target molecules in respect to size, shape, and functional groups. Herein, based on the high selectivity of MIPs and the fluorescence properties of the β-NaYF₄:Yb3+, Er3+ upconversion nanoparticles, MIPs with both specificity and fluorescent signals are fabricated to recognize trace sterigmatocystin (ST) with high selectivity and sensitivity. The structure analogue of ST, 1,8-dihydroxyanthraquinone (DT), was employed as the template molecule, acrylamide as the functional monomer, 3-methacryloyloxypropyltrimethoxysilane as the crosslinking agent, and a new molecular imprinting technique of non-aqueous sol-gel method is used to synthesize a molecularly imprinted material with high selectivity to ST. Under optimal conditions, the fluorescence enhancement of fluorescent MIPs increased as the concentration of ST increased. In the range of 0.05⁻1.0 mg L-1, fluorescence enhancement and the concentration showed a good linear relationship with a detection limit of 0.013 mg L-1. Real sample analysis achieved the recoveries of 83.8⁻88.8% (RSD 5.1%) for rice, 82.1⁻87.5% (RSD 4.6%) for maize, and 80.6⁻89.2% (RSD 3.0%) for soybeans, respectively, revealing the feasibility of the developed method.

Simultaneous Visualization and Quantitation of Multiple Steroid Hormones Based on Signal-Amplified Biosensing with Duplex Molecular Recognition

The simultaneous quantitation of multiple steroid hormones in real time is of great importance in medical diagnosis. In this study, a portable hormone biosensor based on duplex molecular recognition coupled with a signal-amplified substrate was successfully developed for the simultaneous visualization and quantitation of multiple steroid hormones. Aptamer-functionalized upconversion nanoparticles (UCNPs) with different emission peaks are immobilized on the photonic crystal (PC) substrate as the nanoprobes, leading to the specific and simultaneous assay of multiple steroid hormones. Coupled with the luminescence-enhanced effect of the PC substrate, nanomolar quantification limits of multiple hormones are achieved. This well-designed biosensor is also promising in the quantification of multiple hormones in serum samples. The amplified luminescence signals can be visualized with the naked eye and captured by an unmodified phone camera. This hormone quantitation biosensor exhibits the advantages of multi-detection, visualization, high sensitivity, and selectivity for potential applications in clinical disease diagnosis.

An All-Nanocrystal Biosensing System for In Vitro Detection of STAT3 Oligonucleotides

Lanthanide-doped nanocrystals have shown great promise in bio-detection due to their outstanding luminescent properties, including large Stokes shift and sharp emission bands. Herein, we describe an in vitro detection of STAT3 by using an all-nanocrystal biosensing system that takes advantage of inter-particle energy transfer between two types of lanthanide-doped nanocrystals. We investigate the effect of nanocrystal size on the sensing performance and find that smaller nanocrystals offer a lower detection limit and larger dynamic range. As STAT3 is identified as an oncogene aberrantly activated and expressed in malignant transformation and tumorigenesis, our study thus holds promise for cancer diagnosis and therapy.

Identification and imaging of leukemia cells using dual-aptamer-functionalized graphene oxide complex

Acute lymphoblastic leukemia is the most common malignancy in children. Patient improvement completely depends on the diagnosis of acute lymphoblastic leukemia. So there is a great demand for diagnosis of acute lymphoblastic leukemia. In this study, a novel assay based on dual-aptamer (Sgc8c and ATP aptamers)-functionalized graphene oxide (DAFGO) complex was designed for the identification of Molt-4 cells (human acute lymphoblastic leukemia T-cell). This assay relies on the internalization of DAFGO complex into Molt-4 cells, but not into U266 cells, using Sgc8c aptamer as molecular recognition probe, and release of FAM-labeled ATP aptamer from the complex in the presence of high amounts of ATP in lysosome, leading to a strong fluorescence emission. Formation of DAFGO complex was analyzed by fluorometric analysis and gel retardation assay. The internalization of complex was monitored by flow cytometry and fluorescence microscopy in Molt-4 (target) and U266 cells (nontarget) with DAFGO complex. Our results showed that the developed complex was efficiently internalized into target cells and induced a strong fluorescence emission.

Stability, transport and ecosystem effects of graphene in water and soil environments

Graphene nanomaterials (GMs), such as graphene oxide (GO) and reduced graphene oxide (rGO), have been widely applied in various fields. Due to the rapid increase in production and application, the inevitable release of GMs into water and soil environments poses potential health and ecosystem risks. Upon exposure, the behavior, transport, and fate of GMs may be altered after interacting with the relevant environmental conditions. GMs can affect the microbial communities as well. Thus, it is imperative to understand the interaction between the GMs and the environmental systems for predicting their risks. For this purpose, this review highlights the influence of the most relevant environmental factors on the stability, aggregation, and transformation of GMs in aquatic environments. Moreover, the transport of GMs and microbial communities changes have also been presented based on the recent findings. To the best of our knowledge, this review covered most of the recent related studies and will allow for accurate predictions of the fate and risks associated with GMs. In consideration of the diversity of GMs and the complexity of environmental factors, further studies should be focused on their inherent properties and amicable development.

Synergetic Effects of Combined Nanomaterials for Biosensing Applications

Nanomaterials have become essential components for the development of biosensors since such nanosized compounds were shown to clearly increase the analytical performance. The improvements are mainly related to an increased surface area, thus providing an enhanced accessibility for the analyte, the compound to be detected, to the receptor unit, the sensing element. Nanomaterials can also add value to biosensor devices due to their intrinsic physical or chemical properties and can even act as transducers for the signal capture. Among the vast amount of examples where nanomaterials demonstrate their superiority to bulk materials, the combination of different nano-objects with different characteristics can create phenomena which contribute to new or improved signal capture setups. These phenomena and their utility in biosensor devices are summarized in a non-exhaustive way where the principles behind these synergetic effects are emphasized.

Oligonucleotide Sensor Based on Selective Capture of Upconversion Nanoparticles Triggered by Target-Induced DNA Interstrand Ligand Reaction

We present a sensor that exploits the phenomenon of upconversion luminescence to detect the presence of specific sequences of small oligonucleotides such as miRNAs among others. The sensor is based on NaYF₄:Yb,Er@SiO₂ nanoparticles functionalized with ssDNA that contain azide groups on the 3' ends. In the presence of a target sequence, interstrand ligation is possible via the click-reaction between one azide of the upconversion probe and a DBCO-ssDNA-biotin probe present in the solution. As a result of this specific and selective process, biotin is covalently attached to the surface of the upconversion nanoparticles. The presence of biotin on the surface of the nanoparticles allows their selective capture on a streptavidin-coated support, giving a luminescent signal proportional to the amount of target strands present in the test samples. With the aim of studying the analytical properties of the sensor, total RNA samples were extracted from healthy mosquitoes and were spiked-in with a specific target sequence at different concentrations. The result of these experiments revealed that the sensor was able to detect 10^-17 moles per well (100 fM) of the target sequence in mixtures containing 100 ng of total RNA per well. A similar limit of detection was found for spiked human serum samples, demonstrating the suitability of the sensor for detecting specific sequences of small oligonucleotides under real conditions. In contrast, in the presence of noncomplementary sequences or sequences having mismatches, the luminescent signal was negligible or conspicuously reduced.

Quantitative Fluorescence Quenching on Antibody-conjugated Graphene Oxide as a Platform for Protein Sensing

We created an immunosensing platform for the detection of proteins in a buffer solution. Our sensing platform relies on graphene oxide (GO) nanosheets conjugated with antibodies to provide quantitative binding sites for analyte proteins. When analyte proteins and standard fluorescein-labelled proteins are competing for the binding sites, the assay exhibits quantitative fluorescence quenching by GO for the fluorescein-labelled proteins as determined by the analyte protein concentration. Because of this mechanism, measured fluorescence intensity from unquenched fluorescein-labelled protein was shown to increase with an increasing analyte protein concentration. As an alternative to the conventional enzyme-linked immunosorbent assay (ELISA), our method does not require an enzyme-linked second antibody for protein recognition and the enzyme for optical signal measurement. Thus, it is beneficial with its low cost and fewer systematic errors caused by the series of antigen-antibody recognition steps in ELISA. Immune globulin G (IgG) was introduced as a model protein to test our method and our results showed that the limit of detection for IgG was 4.67 pmol mL^-1 in the buffer solution. This sensing mechanism could be developed into a promising biosensor for the detection of proteins, which would broaden the spectrum of GO applications in both analytical biochemistry and clinical diagnosis.

Endowing a triarylboron compound showing ACQ with AIE characteristics by transforming its emissive TICT state to be dark

A triarylboron-based AIE fluorophore, TAB-AIE-FL, was designed and synthesized by introducing an electron acceptor to boost charge separation, transforming its TICT state from bright emission to dark.

Increasing the sensitivity and selectivity of a GONS quenched probe for an mRNA assay assisted with duplex specific nuclease

The authors report a new graphene oxide nanosheet (GONS) based fluorescence method for mRNA assay with duplex-specific nuclease (DSN)-assisted signal amplification.

A novel, rapid, and sensitive homogeneous sandwich detection method of Glypican-3 as a serum marker for hepatocellular carcinoma

Based on multiple interactions and fluorescence quenching, we report a novel homogeneous detection method for Glypican-3 which shows a series of significant advantages, and has great potential in the clinical diagnosis of hepatocellular carcinoma and proteoglycan detection.

Fluorometric “Turn-On” glucose sensing through the in situ generation of silver nanoclusters

A fluorometric “turn-on” glucose detection is performed based on the Fenton reaction which can trigger the generation of Ag nanoclusters.

A ratiometric nanoprobe consisting of up-conversion nanoparticles functionalized with cobalt oxyhydroxide for detecting and imaging ascorbic acid

A new ratiometric probe based on up-conversion nanoparticles displayed excellent selectivity and pronounced sensitivity in the detection of ascorbic acid.

Theranostic Upconversion Nanobeacons for Tumor mRNA Ratiometric Fluorescence Detection and Imaging-Monitored Drug Delivery

Remote optical detection and imaging of specific tumor-related biomarkers and simultaneous activation of therapy according to the expression level of the biomarkers in tumor site with theranostic probes should be an effective modality for treatment of cancers. Herein, an upconversion nanobeacon (UCNPs-MB/Dox) is proposed as a new theranostic nanoprobe to ratiometrically detect and visualize the thymidine kinase 1 (TK1) mRNA that can simultaneously trigger the Dox release to activate the chemotherapy accordingly. UCNPs-MB/Dox is constructed with the conjugation of a TK1 mRNA-specific molecular beacon (MB) bearing a quencher (BHQ-1) and an alkene handle modified upconversion nanoparticle (UCNP) through click reaction and subsequently loading with a chemotherapy drug (Dox). With this nanobeacon, quantitative ratiometric upconversion detection of the target with high sensitivity and selectivity as well as the target triggered Dox release in vitro is demonstrated. The sensitive and selective ratiometric detection and imaging of TK1 mRNA under the irradiation of near infrared light (980 nm) and the mRNA-dependent release of Dox for chemotherapy in the tumor MCF-7 cells and A549 cells are also shown. This work provides a smart and robust platform for gene-related tumor theranostics.

Fluorescence resonance energy transfer biosensor between upconverting nanoparticles and palladium nanoparticles for ultrasensitive CEA detection

An ultrasensitive biosensor for carcinoembryonic antigen (CEA) was constructed based on fluorescence resonance energy transfer (FRET) between upconverting nanoparticles (UCPs) and palladium nanoparticles (PdNPs). PdNPs was synthesized by the addition of a solution of Na2PdCl4 into a mixture of N2H4·H2O as the reducing agent and 11-mercaptoundecanoic acid (MUDA) as the stabilizer. The CEA aptamer (5'-NH2-ATACCAGCTTATTCAATT-3') was conjugated to hexanedioic acid (HDA) modified UCPs (HDA-UCPs) through an EDC-NHS coupling protocol. The coordination interaction between nitrogen functional groups of the CEA aptamer and PdNPs brought UCPs and PdNPs in close proximity, which resulted in the fluorescence quenching of UCPs to an extent of 85%. And the non-specific fluorescence quenching caused by PdNPs towards HDA-UCPs was negligible. After the introduction of CEA into the UCPs-CEA aptamer-PdNPs fluorescence quenching system, the CEA aptamer preferentially combined with CEA accompanied by the conformational change which weakened the coordination interaction between the CEA aptamer and PdNPs. So fluorescence recovery of UCPs was observed and a linear relationship between the fluorescence recovery of UCPs and the concentration of CEA was obtained in the range from 2pg/mL to 100pg/mL in the aqueous buffer with the detection limit of 0.8pg/mL. The ultrasensitive detection of CEA was also realized in diluted human serum with a linear range from 4pg/mL to 100pg/mL and a detection limit of 1.7pg/mL. This biosensor makes the most of the high quenching ability of PdNPs towards UCPs with negligible non-specific fluorescence quenching and has broad application prospects in biochemistry.

DNA-stabilized silver nanoclusters and carbon nanoparticles oxide: A sensitive platform for label-free fluorescence turn-on detection of HIV-DNA sequences

Based on the remarkable difference between the interactions of carbon nanoparticles (CNPs) oxide with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA), and the fact that fluorescence of DNA-stabilized silver nanoclusters (AgNCs) can be quenched by CNPs oxide, DNA-functionalized AgNCs were applied as label-free fluorescence probes and a novel fluorescence resonance energy transfer (FRET) sensor was successfully constructed for the detection of human immunodeficiency virus (HIV) DNA sequences. CNPs oxide were prepared with the oxidation of candle soot, hence it is simple, time-saving and low-cost. The strategy of dual AgNCs probes was applied to improve the detection sensitivity by using dual- probe capturing the same target DNA in a sandwich mode and as the fluorescence donor, and using CNPs oxide as the acceptor. In the presence of target DNA, a dsDNA hybrid forms, leading to the desorption of the ssDNA-AgNCs probes from CNPs oxide, and the recovering of fluorescence of the AgNCs in a HIV-DNA concentration-dependent manner. The results show that HIV-DNA can be detected in the range of 1-50nM with a detection limit of 0.40nM in aqueous buffer. The method is simple, rapid and sensitive with no need of labeled fluorescent probes, and moreover, the design of fluorescent dual-probe makes full use of the excellent fluorescence property of AgNCs and further improves the detection sensitivity.

Atomic Oxygen Tailored Graphene Oxide Nanosheets Emissions for Multicolor Cellular Imaging

Graphene oxide (GO) has been widely used as a fluorescence quencher, but its luminescent properties, especially tailor-made controlling emission colors, have been seldom reported due to its heterogeneous structures. Herein, we demonstrated a novel chemical oxidative strategy to tune GO emissions from brown to cyan without changing excitation wavelength. The precise tuning is simply achieved by varying reaction times of GO nanosheets in piranha solution, but there is no need for complex chromatography separation procedures. With increasing reaction times, oxygen content on the lattice of GO nanosheets increased, accompanied by the diminution of their sizes and sp(2) conjugation system, resulting in an increase of emissive carbon cluster-like states. Thereby, the luminescent colors of GO were tuned from brown to yellow, green, and cyan, and its fluorescent quantum yields were enhanced. The obtained multicolored fluorescent GO nanosheets would open plenty of novel applications in cellular imaging and multiplex encoding analysis.

Paper-based upconversion fluorescence resonance energy transfer biosensor for sensitive detection of multiple cancer biomarkers

A paper-based upconversion fluorescence resonance energy transfer assay device is proposed for sensitive detection of CEA. The device is fabricated on a normal filter paper with simple nano-printing method. Upconversion nanoparticles tagged with specific antibodies are printed to the test zones on the test paper, followed by the introduction of assay antigen. Upconversion fluorescence measurements are directly conducted on the test zones after the antigen-to-antibody reactions. Furthermore, a multi-channel test paper for simultaneous detection of multiple cancer biomarkers was established by the same method and obtained positive results. The device showed high anti-interfere, stability, reproducible and low detection limit (0.89 ng/mL), moreover it is very easy to fabricate and operate, which is a promising prospect for a clinical point-of-care test.

An efficient signal-on aptamer-based biosensor for adenosine triphosphate detection using graphene oxide both as an electrochemical and electrochemiluminescence signal indicator

An efficient aptasensor was developed in which graphene oxide (GO) was employed as an indicator for both electrochemical impedance spectroscopy and electrochemiluminescence (ECL) signal generation. The aptasensor was fabricated by self-assembling the ECL probe of a thiolated adenosine triphosphate binding aptamer (ABA) tagged with a Ru complex (Ru(bpy)3(2+) derivatives) onto the surface of gold nanoparticle (AuNP) modified glassy carbon electrode (GCE). ABA immobilized onto AuNP modified GCE could strongly adsorb GO due to the strong π-π interaction between ABA and graphene oxide; ECL quenching of the Ru complex then takes place because of energy transfer and electron transfer, and a large increase of the electron transfer resistance (Ret) of the electrode. While in the presence of target adenosine triphosphate (ATP), the ABA prefers to form ABA-ATP bioaffinity complexes, which have weak affinity to graphene oxide and keep the graphene oxide away from the electrode surface, thus allowing the ECL signal enhancement, and in conjunction with the decrease of the Ret. Because of the high ECL quenching efficiency, unique structure, and electronic properties of graphene oxide, the Ret and ECL intensity versus the logarithm of ATP concentration was linear in the wide range from 10 pM to 10 nM with an ultra-low detection limit of 6.7 pM to 4.8 pM, respectively. The proposed aptasensor exhibited excellent reproducibility, stability, and outstanding selectivity, and ATP could be effectively distinguished from its analogues. More significantly, this efficient ECL aptasensor strategy based on GO acting both as an electrochemical and ECL signal indicator is general and can be easily extended to other biological binding events.

A novel aptamer-mediated CuInS2quantum dots@graphene oxide nanocomposites-based fluorescence “turn off–on” nanosensor for highly sensitive and selective detection of kanamycin

A novel aptamer-mediated fluorescence “turn off–on” nanosensor for highly sensitive and selective detection of kanamycin using CuInS₂quantum dots@graphene oxide.

Graphdiyne oxide as a platform for fluorescence sensing

Graphdiyne (GD), a new kind of two-dimensional carbon allotrope consisting of a hexagonal ring and a diacetylenic linkage unit, is observed to exhibit a high fluorescence quenching ability and can be used as a new platform for fluorescence sensing, where GD oxide, the oxidized form of GD, is found to exhibit higher quenching ability than GD.