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Carbon dots have promising prospects for analytical and monitoring purposes, but are greatly hindered by the aggregation-induced luminescence quenching owing to the π–π interaction or the non-radiation-excited radical complex formation. Herein hydrothermally prepared orange-yellow fluorescent carbon dots (O-CDs) show an aggregation-induced fluorescence enhancement (AIFE) with Cu2+ owing to the complexation of Cu(II) and the O-CDs. Cu2+ was then sensitively and selectively detected in the linear range from 0.02 to 30 μM with the detection limit of 14 nM, making the detection of Cu2+ in fresh water and E. coli lysate successful, showing that the as-prepared O-CDs could be well applied to the environmental monitoring of heavy metals. [ABSTRACT FROM AUTHOR]

The expression level of nucleic acids is closely related to a variety of diseases. Herein, a highly sensitive detection of a nucleic acid based on a CoOOH-luminol chemiluminescence (CL) system without the addition of oxidants was proposed by the toehold-mediated strand displacement reaction (TSDR) and the liposome dual signal amplification strategy with the hybrid probe formed by linking soft nanoballs (SNBs) to magnetic beads (MBs) through DNA hybridization. Inspired by the free radical scavenging effect of the as-prepared carbon dots (CDs), CDs were successfully employed to quench the CL intensity of the CoOOH-luminol system. And the CDs were further encapsulated into liposomes to construct SNBs, which avoided the complex modification of CDs to maintain their original properties, as well as loaded a large number of CDs to scavenge free radicals to achieve signal amplification. Based on this, target DNA (tDNA) could be sensitively detected based on the reduced CL intensity, which achieved a dynamic detection range from 0.1 nM to 20 nM with a limit of detection as low as 59 pM (3σ/k), showing amazing promise in the biosensing of nucleic acid biomarkers. [ABSTRACT FROM AUTHOR]

DNA-based nanomachines have aroused tremendous interest because of their potential applications in bioimaging, biocomputing, and diagnostic treatment. Herein, we constructed a novel exonuclease III-propelled and signal-amplified stochastic DNA walker that autonomously walked on a spherical particle-based 3D track through a burnt-bridge mechanism, during which nanosurface energy transfer (NSET) occurred between the fluorescent dye modified on hairpin DNA and the surface of gold nanoparticles (AuNPs). As a proof of concept, this stochastic DNA walker achieves prominent detection performance of HIV DNA in the range of 0.05–1.2 nM with a detection limit of 12.7 pM and satisfactory recovery in blood serum, showing high promise in biosensing applications with complicated media. [ABSTRACT FROM AUTHOR]

Qualitative and quantitative determination of lysozyme concentrations in urine and serum with high selectivity and sensitivity is important for diagnosing the progression of several diseases. In this report, we devised an improved method for specifically detecting lysozyme by combining magnetic nanoparticles (for separation and enrichment), an aptamer (for selective binding of lysozyme) and strongly scattering silver nanoparticles (AgNPs, for detection by light scattering, but also providing another level of selectivity due to their electrostatic binding with lysozyme). In this system, 0.4–30 nM lysozyme could be simply detected owing to the decreased light scattering of AgNPs in solution after magnetic separation, with a detection limit of 100 pM. In addition, lysozyme was also able to be semi-quantified by using the dark-field light scattering images of AgNPs after enrichment by the MNP–apt–lysozyme complex. Moreover, this design shows great promise for the robust and reliable detection of lysozyme in real samples, with a recovery rate ranging from 98.6% to 101.3% in human serum samples. Therefore, this assay provided robust measurements with good specificity, sensitivity, and tolerance of changes in the sample matrix. We expect that this MNP-based aptasensor may find utility in the accurate diagnosis of lysozyme-related diseases. [ABSTRACT FROM AUTHOR]

Silver nanoclusters (AgNCs) have gained considerable attention over a wide range from chemical detection to bioimaging applications. Herein we developed a facile way to synthesize water-soluble, intense fluorescent targetable AgNCs with yellow-emission by using DNA via a chemical reduction method. The sequence of DNA was designed to contain two fragments, one of which is the DNA aptamer fragment which can selectively bind to the target, and the other is rich in cytosine sequence fragments that can result in a high quantum efficiency. The as-prepared targetable AgNCs (Apt-AgNCs) through the reduction of silver ions (Ag+) by NaBH4 have a very strong fluorescence emission, which, was greatly quenched upon specific binding to prion protein (PrPC). As a result, Apt-AgNCs were demonstrated as a novel, effective and sensitive probe for both detection and intracellular fluorescent imaging with high selectivity through the strong binding affinity between the aptamer and its target. [ABSTRACT FROM AUTHOR]

A new spectrofluorometric method for cellular prion protein (PrPC) was developed based on the regulation of N,N′-bis[3,3′-(dimethylamino)propylamine]-3,4,9,10-perylenetetracarboxylic diimide (DAPER) fluorescence. As a perylene derivative, DAPER emits strong fluorescence in the form of free monomer in aqueous medium, but not in the form of aggregates. In this contribution, we found that the aptamer of PrPC could induce the aggregation of DAPER, and the bright fluorescence of DAPER was completely quenched. The quenched fluorescence, however, was recovered if PrPC was further added, which was ascribed to the specific binding of PrPC to its aptamer and the releasing of free DAPER monomers. This signalling mechanism makes it possible to detect PrPC by fluorescence spectroscopy. The assay allows the selective determination of PrPC in aqueous solution with high sensitivity and exhibits a good linear range from 0.4 to 1.6 nmol L−1. Moreover, this probe can be applied to monitor the level of PrPC in human urine samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Fluorescence anisotropy (FA) has attracted considerable attention, but it has been rarely applied for the detection of small molecules and metal ions because they are too small to induce evident FA changes. Although some mass amplifying strategies have been developed, the recognition probes need to be covalently modified with the fluorescent dyes, which is complex and expensive. To overcome this limitation, a new simple, label-free and cost-effective method for the sensitive detection of potassium ion (K(+)), by using graphene oxide (GO) as FA enhancer, a G-rich single stranded DNA (ssDNA) as recognition probe and acridine orange (AO) as FA reporting fluorophore, was established in this paper. In the absence of K(+), both ssDNA and AO are adsorbed on the surface of GO, and the FA of AO is enhanced greatly because the rotation of AO is coupled with the entire formation. After the addition of K(+), the ssDNA self-associates into the G-quadruplex structure. Then, AO can bind with the formed G-quadruplex strongly, keeping away from the surface of GO, and the FA of AO decreases significantly because of the relatively small size of the complex of AO and G-quadruplex. Thus K(+) can be detected sensitively in the range of 10 μM-2 mM based on the evidently decreased FA. This method is a further improvement of the previous reported mass amplifying strategies because it does not require any covalent labelling of the recognition probe, and it can be potentially applied for detection of a variety of other targets.