Surface-enhanced Raman scattering assay combined with autonomous DNA machine for detection of specific DNA and cancer cells

An ultrasensitive surface-enhanced Raman scattering (SERS) detection system based on DNA machine isothermal amplification is reported to detect a specific DNA sequence for the first time and was successfully applied to detect cancer cells.     

Characterization of new fluorescent peroxidase substrates

The reagents Lumigen PS-1 and Lumigen PS-3 were originally developed as chemiluminescent substrates for ultrasensitive detection of horseradish peroxidase (HRP) in homogeneous solution and membrane blotting assays. However, an additional unique feature of these acridan-based reagents is the generation of a fluorescent species on reaction with peroxidase, a property which has been termed as chemifluorescence. These reagents, therefore, represent the first dual-use substrates enabling both chemiluminescent and fluorescent detection. We have developed several additional acridan-based substrates for fluorescent detection of HRP which are capable of subattomole detection sensitivity. By varying several structural parameters within the class of compounds we have produced substrates which either produce fluorescence alone or both chemiluminescence and fluorescence.     

In Situ Generation of AgI Quantum Dots by the Confinement of A Supramolecular Polymer Network: A Novel Approach for Ultrasensitive Response

A novel approach for in situ generation of AgI quantum dots by the confinement of a pillar[5]arene‐based supramolecular polymer network has been successfully developed. The supramolecular polymer network ( SPN‐QP ) was constructed by using a bis‐8‐hydroxyquinoline‐modified pillar[5]arene derivative as a host ( H‐QP ) and a bis‐pyridinium‐modified decane as guest ( G‐PD ). The SPN‐QP shows ultrasensitive response for Ag⁺. The limit of detection is about 7.44×10^?9 M.^.Interestingly, when I^? was added to the SPN‐QP +Ag⁺ system, an unexpected strong warm‐white fluorescence emission was observed. After carefu investigation, we found that the strong warm‐white fluorescence emission could be attributed to the in situ formation of AgI quantum dots under the confinement of the supramolecular polymer network ( SPN‐QP ). Based on this approach, ultrasensitive detection of I^? was realized. The limit of detection for I^? is 4.40×10^?9 M. This study provides a new way for the preparation of quantum dots under the confinement of supramolecular polymer network as well as ultrasensitive detection of ions by in situ formation of quantum dots.     

Electrochemical aptasensor for the determination of bisphenol A in drinking water

We present an electrochemical aptasensor for rapid and ultrasensitive determination of the additive bisphenol A (BPA) and for screening drinking water for the presence of BPA. A specific aptamer against BPA and its complementary DNA probe were immobilized on the surface of a gold electrode via self-assembly and hybridization, respectively. The detection of BPA is mainly based on the competitive recognition of BPA by the immobilized aptamer on the surface of the electrode. The electrochemical aptasensor enables BPA to be detected in drinking water with a limit of detection as low as 0.284 pg?mL^?1 in less than 30 min. This extraordinary sensitivity makes the method a most powerful tool for on-site monitoring of water quality and food safety.

Signal amplification strategies for DNA and protein detection based on polymeric nanocomposites and polymerization: A review

Demand is increasing for ultrasensitive bioassays for disease diagnosis, environmental monitoring and other research areas. This requires novel signal amplification strategies to maximize the signal output. In this review, we focus on a series of significant signal amplification strategies based on polymeric nanocomposites and polymerization. Some common polymers are used as carriers to increase the local concentration of signal probes and/or biomolecules on their surfaces or in their interiors. Some polymers with special fluorescence and optical properties can efficiently transfer the excitation energy from a single site to the whole polymer backbone. This results in superior fluorescence signal amplification due to the resulting collective effort (integration of signal). Recent polymerization-based signal amplification strategies that employ atom transfer radical polymerization (ATRP) and photo-initiated polymerization are also summarized. Several distinctive applications of polymers in ultrasensitive bioanalysis are highlighted.     

An ultrasensitive electrochemical sensor for the mercuric ion via controlled assembly of SWCNTs

An ultrasensitive "turn-on" electrochemical sensor for the Hg(2+) ion was proposed based on the T-Hg(2+)-T coordination chemistry and the controlled assembly of SWCNTs on the MHA/SAM-modified gold electrode.     

The back photoreaction of the M intermediate in the photocycle of bacteriorhodopsin: mechanism and evidence for two M species

The back photoreaction of the M intermediate in the photocycle of bacteriorhodopsin is investigated both for the native pigment and its D96N mutant. The experimental setup is based on creating the M intermediate by a first pulse, followed by a (blue) laser pulse which drives the back photoreaction of M. Experiments are carried out varying the delay between the two pulses, as well as the temperature over the -25 degrees C-20 degrees C range. It is found that the kinetic patterns of the M back photoreaction change with time after the generation of this intermediate. The data provide independent evidence for the suggestion of a photocycle mechanism based on two distinct M intermediates. They are thus in keeping with the consecutive model of Varo and Lanyi (Biochemistry 30, 5016-5022; 1991), although they cannot exclude other models such as those based on branched or parallel cycles. More generally, we offer a "photochemical" approach to discriminating between intermediate stages in the photocycle which does not depend on spectroscopic and/or kinetic data. While markedly affecting the rate of the M --> N transition in the photocycle, the rate of the thermal step in back photoreaction of M, at both room and low temperatures, is not significantly affected by the D96N mutation. It is proposed that while Asp 96 is the Schiff-base protonating moiety in the M --> N transition, another residue (most probably Asp 85) reprotonates the Schiff base following light absorption by M.     

Monolayer Two‐dimensional Molecular Crystals for an Ultrasensitive OFET‐based Chemical Sensor

The sensitivity of conventional thin‐film OFET‐based sensors is limited by the diffusion of analytes through bulk films and remains the central challenge in sensing technology. Now, for the first time, an ultrasensitive (sub‐ppb level) sensor is reported that exploits n‐type monolayer molecular crystals (MMCs) with porous two‐dimensional structures. Thanks to monolayer crystal structure of NDI3HU‐DTYM2 (NDI) and controlled formation of porous structure, a world‐record detection limit of NH₃ (0.1 ppb) was achieved. Moreover, the MMC‐OFETs also enabled direct detection of solid analytes of biological amine derivatives, such as dopamine at an extremely low concentration of 500 ppb. The remarkably improved sensing performances of MMC‐OFETs opens up the possibility of engineering OFETs for ultrasensitive (bio)chemical sensing.     

A Label-free Fluorescent Aptasensor for Turn-on Monitoring Ochratoxin A Based on AIE-active Probe and Graphene Oxide

A label-free fluorescent aptasensor for specific and ultrasensitive monitoring ochratoxin A(OTA) was developed using the specific aptamer of OTA(OSA) as recognition element, an aggregation-induced emission(AIE) molecule(a 9,10-distyrylanthracene with two ammonium groups, DSAI) as a fluorescent probe, and graphene oxide(GO) as a quencher. In the absence of OTA, the AIE probe DSAI and OSA complex(DSAI/OSA) is adsorbed on the GO surface, and the fluorescence of DSAI will be quenched efficiently via the fluorescence resonance energy transfer(FRET) from DSAI to GO. Upon the OTA addition, a more stable complex(OSA-OTA) is formed and released from GO. Meanwhile, DSAI and OSA-OTA can form a new complex(DSAI/OSA-OTA), then the fluorescent signal of DSAI recovers gradually. Therefore, by introducing GO and DSAI, the fluorescence signal of DSAI can be easily turned from "off" to "on" after the addition of OTA, and the ultrasensitive detection of OTA by monitoring the change of the fluorescence signal of DSAI can be readily realized. The detection limit of the assay can reach 0.324 nmol/L with a linear detection range of 10-200 nmol/L. And the aptasensor exhibits high selectivity for OTA against other analogues. Moreover, it has been successfully applied for the detection of OTA in red wine samples.     

All on size-coded single bead set: a modular enrich-amplify-amplify strategy for attomolar level multi-immunoassay

Ultrasensitive protein analysis is of great significance for early diagnosis and biological studies. The core challenge is that many critical protein markers at extremely low aM to fM levels are difficult to accurately quantify because the target-induced weak signal may be easily masked by the surrounding background. Hence, we propose herein an ultrasensitive immunoassay based on a modular Single Bead Enrich-Amplify-Amplify (SBEAA) strategy. The highly efficient enrichment of targets on only a single bead (enrich) could confine the target-responsive signal output within a limited tiny space. Furthermore, a cascade tyramide signal amplification design enables remarkable in situ signal enhancement just affixed to the target. As a result, the efficient but space-confined fluorescence deposition on a single bead will significantly exceed the background and provide a wide dynamic range. Importantly, the SBEAA system can be modularly combined to meet different levels of clinical need regarding the detection sensitivity from aM to nM. Finally, a size-coded SBEAA set (SC-SBEAA) is also designed that allows ultrasensitive multi-immunoassay for rare samples in a single tube.

A modular single bead enrich-amplify-amplify strategy is proposed for simultaneous detection of multiple proteins at the aM level.     

Reversing current rectification to improve DNA‐sensing sensitivity in conical nanopores

Herein, we report the ultrasensitive DNA detection through designing an elegant nanopore biosensor as the first case to realize the reversal of current rectification direction for sensing. Attributed to the unique asymmetric structure, the glass conical nanopore exhibits the sensitive response to the surface charge, which can be facilely monitored by ion current rectification curves. In our design, an enzymatic cleavage reaction was employed to alter the surface charge of the nanopore for DNA sensing. The measured ion current rectification was strongly responsive to DNA concentrations, even reaching to the reversed status from the negative ratio (?6.5) to the positive ratio (+16.1). The detectable concentration for DNA was as low as 0.1 fM. This is an ultrasensitive and label‐free DNA sensing approach, based on the rectification direction‐reversed amplification in a single glass conical nanopore.     

Valency‐Controlled Framework Nucleic Acid Signal Amplifiers

Weak ligand–receptor recognition events are often amplified by recruiting multiple regulatory biomolecules to the action site in biological systems. However, signal amplification in in vitro biomimetic systems generally lack the spatiotemporal regulation in vivo. Herein we report a framework nucleic acid (FNA)‐programmed strategy to develop valence‐controlled signal amplifiers with high modularity for ultrasensitive biosensing. We demonstrated that the FNA‐programmed signal amplifiers could recruit nucleic acids, proteins, and inorganic nanoparticles in a stoichiometric manner. The valence‐controlled signal amplifier enhanced the quantification ability of electrochemical biosensors, and enabled ultrasensitive detection of tumor‐relevant circulating free DNA (cfDNA) with sensitivity enhancement of 3–5 orders of magnitude and improved dynamic range.     

A novel nanoaggregation detection technique of TNT using selective and ultrasensitive nanocurcumin as a probe

Here, for the first time, we designed an ultrasensitive nanocurcumin based nanomaterials surface energy transfer (NSET) probe for detection of trace amount of TNT with excellent sensitivity (1 nM) and selectivity over other nitro explosives via nanoaggregation and we found the largest fluorescent enhancement to date for sensing TNT (upto 800 fold).     

Highly sensitive detection of lead(II) ion using multicolor CdTe quantum dots

Multicolor and water-soluble CdTe quantum dots (QDs) were synthesized with thioglycolic acid (TGA) as stabilizer. These QDs have a good size distribution, display high fluorescence quantum yield, and can be applied to the ultrasensitive detection of Pb(II) ion by virtue of their quenching effect. The size of the QDs exerts a strong effect on sensitivity, and quenching of luminescence is most effective for the smallest particles. The quenching mechanism is discussed. Fairly selective detection was accomplished by utilizing QDs with a diameter of 1.6?nm which resulted in a detection limit of 4.7?nmol?L^?1 concentration of Pb(II). The method was successfully applied to the determination of Pb(II) in spinach and citrus leaves, and the results are in good agreement with those obtained with atomic absorption spectrometry.

Electrochemical detection of DNA hybridization based on carbon-nanotubes loaded with CdS tags

An effective method for amplifying electrical detection of DNA hybridization based on carbon-nanotubes (CNT) carrying a large number of CdS particle tracers is described. Such use of CNT amplification platforms is combined with an ultrasensitive stripping-voltammetric detection of the dissolved CdS tags following dual hybridization events of a sandwich assay on a streptavidin modified 96-well microplate. Anchoring of the monolayer-protected quantum dots to the acetone-activated CNT was accomplished via hydrophobic interactions. SEM images indicate that the nanocrystals are attached along the CNT sidewall, with a loading of around 500 particles per CNT. A substantial (500-fold) lowering of the detection limit is obtained compared to conventional single-particle stripping hybridization assays, reflecting the CdS loading on the CNT carrier. A large excess (250-fold) of non-complimentary oligonucleotides have minimal effect on the response. Such use of CNT as carriers for multiple electrochemical tags offers great promise for ultrasensitive detection of other biorecognition events.     

Ultrasensitive,simple and solvent-free micro-assay for determining sulphite preservatives (E220–228) in foods by HS-SDME and UV–vis micro-spectrophotometry

A new method based on headspace single-drop microextraction in combination with UV–vis micro-spectrophotometry has been developed for the ultrasensitive determination of banned sulphite preservatives (E220–228) in fruits and vegetables. Sample acidification was used for SO₂ generation, which is collected onto a 5,5′-dithiobis-(2-nitrobenzoic acid) microdrop for spectrophotometric measurement. A careful study of this reaction was necessary, including conditions for SO₂ generation from different sulphating salts, drop pH, 5,5′-dithiobis-(2-nitrobenzoic acid) concentration and potential interference effects. Variables influencing mass transfer (stirring, sample volume and addition of salt) and microextraction time were also studied. A simple sulphite extraction was carried out, and problems caused by oxidation during the extraction process were addressed. A high enrichment factor (380) allows the determination of low levels of free SO₂ in fruits and vegetables (limit of detection 0.06 μg g^?1, limit of quantification 0.2 μg g^?1) with an adequate precision (repeatability, relative standard deviation 5 %). In addition, the sulphiting process was studied through the monitoring of residual SO₂ in a vegetal sample, thus showing the importance of a sensitive tool for SO₂ detection at low levels.

Ultrasensitive competitive electrochemiluminescence immunoassay for the β-adrenergic agonist phenylethanolamine A using quantum dots and enzymatic amplification

Microchimica Acta - We have designed an ultrasensitive electrochemiluminescence (ECL) immunoassay for the determination of the β-adrenergic agonist phenylethanolamine A (PA). It is based on...     

A simple and ultrasensitive electrochemical DNA biosensor based on DNA concatamers

A simple, ultrasensitive and selective electrochemical DNA biosensor based on DNA concatamers is described, which can detect as low as 100 aM target DNA even in complex samples.     

First examples of stable arenium ions from large methylene-bridged polycyclic aromatic hydrocarbons (PAHs). Directive effects and charge delocalization mode

In connection to a growing interest in developing structure/activity trends in nonalternant polyarenes, we report on the generation and NMR studies of the first series of persistent arenium ions from large methylene-bridged PAHs (mostly 22pi six-fused ring systems). Low-temperature protonation (FSO(3)H/SO(2)ClF) and model nitration (with HNO(3)/HOAc or NO(2)(+) BF(4)(-)) were used as mimic reactions for generation of biological electrophiles. The site(s) of protonation (and nitration) were determined as a function of PAH structure. Charge delocalization mode in the resulting arenium ions of protonation are assessed based on detailed low-temperature NMR studies at 500 MHz. Systems studied were 1-methylcyclopenta[def]phenanthrene 2, 11H-benz[bc]aceanthrylene 8, 5H-benzo[b]cyclopenta[def]chrysene 9, 13H-dibenzo-[bc,l]aceanthrylene 10, 13H-cyclopenta[rst]pentaphene 11, 4H-benzo[b]cyclopenta[mno]chrysene 12, 6H-cyclopenta[ghi]picene 13, 4H-cyclopenta[pqr]picene 14, 4H-cyclopenta[def]dibenz[a,c]anthracene 15. For comparison, dibenzo[a,c]anthracene 16 and dibenzo[a,h]anthracene 17 were also included (Figures 1 and 2). It is shown that the methano-bridge exerts a strong directive effect which diminishes as the bridge moves from the more central "inner" positions to more peripheral "outer" positions. Charge delocalization mode in the resulting carbocations are discussed based on the magnitude of Deltadelta (13)C values. Possible relationships with biological electrophiles formed by epoxide ring opening in the putative metabolites are also considered.