Facile Fluorescence Method Research Articles

Rapid statistical discrimination of fluorescence images of multiple foodborne pathogens using multicolor-emissive carbon dots

The rapid discrimination of multiple foodborne pathogens is vital and challengeable in ensuring food safety. Herein, a facile fluorescence method was developed to distinguish different bacteria using multicolor-emissive carbon dots (CDs) based on confocal laser scanning microscopy (CLSM) and linear discriminant analysis (LDA). The array employs single CDs as receptors and indicators, two pH solutions and three excitation channels as sensing elements for multicolor imaging and recognition of multiple bacteria. Through one-step staining, the CDs were capable of rapid adsorbing onto all bacteria in 1 min with varying affinities. The discrimination ability of the array was markedly enhanced by means of the synergistic recognition of bacteria and CDs across diverse pH levels and three excitation channels. By using LDA, six kinds of bacteria could be well discriminated with the classification accuracy of 100%. Meanwhile, the feasibility has been successfully expanded to mixture and food samples discrimination.

A facile fluorescence method for the effective detection of ampicillin using antioxidant carbon dots with specific fluorescent response to ˙OH.

Monitoring methods for beta-lactam (β-lactam) antibiotics, especially for ampicillin (AMP), with simple operation and sensitivity for realtime applications are highly required. To address this need, antioxidant carbon dots (E-CDs) with excellent fluorescence properties were synthesized using citric acid and ethylenediamine as raw materials. With a quantum yield of 81.97%, E-CDs exhibited a specific and sensitive response to ˙OH. The quenched fluorescence of E-CDs by the formed ˙OH could be restored through a competition reaction with AMP. Leveraging the signal-quenching strategy of E-CDs, H2O2, and Fe2+, a fluorescence signal-on strategy was developed using AMP as the fluorescence recovery agent for the sensitive detection of AMP. The mechanism of the quenching of E-CDs by ˙OH was attributed to the damaging effect of ˙OH on E-CDs. Under optimal conditions, the detection limit of this method for AMP was determined to be 0.38 μg mL-1. This method was successful in drug quality control and the spiked detection of AMP in lake water, milk, and sea cucumber, presenting a viable option for convenient and rapid antibiotic monitoring methods.

A signal-on fluorescence-based strategy for detection of microRNA-21 based on graphene oxide and λ exonuclease-based signal amplification.

MicroRNA (miRNA) expression is perturbed in various diseases. Herein, we have aimed to develop a novel and rapid fluorescence-based assay for detecting microRNA-21 (miR-21) activity based on FAM molecular signal amplification and graphene oxide (GO) quenching. In this system, a single stranded DNA (ssDNA) with a phosphate group at the 5'-end is labeled with a FAM molecular label at the 3'-end. In the presence of miR-21, this ssDNA forms a DNA/RNA duplex, which is cleaved by λ exonuclease (λ-exo), releasing FAM and resulting in fluorescence signal amplification at 530 nm. However, the DNA/RNA duplex is not generated in the absence of miR-21, which impedes λ-exo cleavage; subsequently, GO quenches the fluorescence intensity. The results show a detection limit of 0.02 nM and a wide linear range of 0.02-5 nM. The high sensitivity and easy operability of this assay can be applied for detecting miR-21 during clinical diagnosis of certain diseases and in biological research.

TiO2 nanowires as an effective sensing platform for rapid fluorescence detection of single-stranded DNA and double-stranded DNA

Numerous nanomaterials have been utilized for novel biosensors with sensitivity and selectivity in the last decades due to their intrinsic unique properties. Herein, a facile fluorescence method for nucleic acid detection was developed by employing TiO2 nanowires (NWs) as the sensing platform. The quenching effect of TiO2 NWs to fluorophore-labelled single-stranded DNA (ssDNA) was found to be more significant than that to fluorophore-labelled double-stranded DNA (dsDNA) or triplex DNA probes. More importantly, the whole quenching process was also fast since it just took about ten minutes to reach the equilibrium. Based on the different affinities of TiO2 NWs to ssDNA, dsDNA and triplex DNA probes, the sequence-specific nucleic acids were detected with sensitivity and specificity. Further investigation has demonstrated that the quenching efficiency of TiO2 NWs to long ssDNA was apparently superior than that to short ssDNA. Moreover, the fluorescence from various ssDNA probes labelled with a wide spectrum of fluorescent dyes could also be quenched by TiO2 NWs. These inspiring results reveal that TiO2 NWs could be an excellent universal nanoquencher used in the next-generation biosensors.

Fluorescent monitoring of the reaction kinetics of nonfluorescent molecules enabled by a fluorescent receptor.

A facile fluorescent method was developed to quantitatively monitor the hydrolysis kinetics of nonfluorescent esters by using a fluorecent endo-functionalized molecular tube and its recognition ability towards small polar molecules in water. It is possible to determine the apparent rate constants and study the structure-activity relationship.

A label-free fluorescence method for actin detection based on DNA-templated silver nanoclusters

A facile fluorescence method has been developed for the detection of actin based on an enzyme-responsive DNA-silver nanocluster probe.

A Novel Detection Method of Human Serum Albumin Based on the Poly(Thymine)-Templated Copper Nanoparticles.

In this work, we developed a facile fluorescence method for quantitative detection of human serum albumin (HSA) based on the inhibition of poly(thymine) (poly T)-templated copper nanoparticles (CuNPs) in the presence of HSA. Under normal circumstances, poly T-templated CuNPs can display strong fluorescence with excitation/emission peaks at 340/610 nm. However, in the presence of HSA, it will absorb cupric ion, which will prevent the formation of CuNPs. As a result, the fluorescence intensity will become obviously lower in the presence of HSA. The analyte HSA concentration had a proportional linear relationship with the fluorescence intensity of CuNPs. The detection limit for HSA was 8.2 × 10−8 mol·L−1. Furthermore, it was also successfully employed to determine HSA in biological samples. Thus, this method has potential applications in point-of-care medical diagnosis and biomedical research.

Fluorometric detection of tyrosine and cysteine using graphene quantum dots

A facile fluorescence method has been developed for the detection of tyrosine and cysteine based on graphene quantum dots as a sensitive probe.

Hydrothermal synthesis of blue-emitting silicon quantum dots for fluorescent detection of hypochlorite in tap water

A facile fluorescence method for detecting hypochlorite in tap water with good selectivity and sensitivity has been designed using SiQDs. As low as 0.01 μM of hypochlorite can be detected and the practicability has been investigated in tap water.

A facile fluorescence method for versatile biomolecular detection based on pristine α-Fe2O3 nanoparticle-induced fluorescence quenching

This work investigated the interactions of α-Fe2O3 nanoparticles (NPs) with different structural nucleic acids and their fluorescence quenching ability towards fluorophore-labelled nucleic acid probes. Different from bulk α-Fe2O3 samples, nanoscale α-Fe2O3 particles exhibit the unique properties of strong adsorption and fluorescence quenching to fluorophore-labelled single-stranded DNA (ssDNA) probes. Based on these findings, a facile fluorescence method was developed for versatile quantification of nucleic acids. The size scale of NPs makes a significant impact on this sensing platform. Better selectivity was given by bigger NP (50–100nm)-based nucleic acid-sensing platform compared with smaller NP (30nm)-based one. In the 50–100nm α-Fe2O3 NP-based sensing platform, single nucleotide mismatch or single base-pair mismatch can even be effectively discriminated. The targets of micro-RNA (miRNA), ssDNA and double-stranded DNA (dsDNA) are sensitively detected with detection limits of 0.8nM, 1.1nM and 0.64nM (S/N=3), respectively. Significantly, α-Fe2O3 NPs possess different affinities towards ssDNA probes with different lengths, and can be used as a universal quencher for ssDNA probes labelled with different fluorescent dyes. On the basis of these properties, the pristine α-Fe2O3 NPs hold the potential to be widely utilized in the development of novel biosensors with signal amplification or simultaneous multiple target detection strategies.

A facile fluorescence method for endonuclease detection using exonuclease III-aided signal amplification of a molecular beacon

An exonuclease III (Exo III)-aided signal amplified endonuclease detection strategy was developed by employing a hairpin DNA as the substrate for endonucleases. In the presence of endonucleases, the elaborately designed stem-loop substrate was cleaved into two parts. With the help of Exo III, a single-stranded target of a molecular beacon (MB) probe was released. Subsequently, the MB would hybridize with this target to form a double-stranded DNA, opening its hairpin structure and thereby resulting in the restoration of the fluorescence signal. Owing to the presence of a recessed 3′ terminus in the formed double-stranded DNA, Exo III-aided recyclable cleavage of MBs was achieved. Eventually, an amplified fluorescence signal was observed. As a proof of concept, the fluorescence sensor of endonuclease EcoRI was designed. Under the optimized conditions, the fluorescence intensity is linear with EcoRI activity over the wide range of 1 to 80 U mL−1, with a detection limit of 0.57 U mL−1. Besides, detection of BamHI activity with satisfactory results was achieved by simply changing the endonuclease recognition sequence in the unlabelled substrate, demonstrating that the design concept can be widely adapted to other restriction endonuclease activity analysis.

Sensitive and selective fluorescence determination of trace hydrazine in aqueous solution utilizing 5-chlorosalicylaldehyde

A facile fluorescent method for the determination of hydrazine in aqueous solution with excellent sensitivity was developed. 5-Chlorosalicylaldehyde (CS), a readily commercially available compound, was applied as the derivatization reagent in this work. Under the addition of CS to hydrazine aqueous solution (ethanol/water/acetic acid = 30/66/4), an intense fluorescence enhancement was observed at 570 nm with a large stokes shift of ∼170 nm. Upon the optimal condition, the fluorescence intensity linearly increased with the concentration of hydrazine in the range of 0.2 and 9.3 μM with a correlation coefficient of R 2 = 0.9995 ( n = 10) and a detection limit of 0.08 μM. The R.S.D. was 2.0% ( n = 5). Determination of hydrazine in river and drinking water samples was successfully performed. Hydrazine vapor sensing by the proposed method was also reported.