CRISPR/Cas12a-Mediated Aptasensor Based on Tris-(8-hydroxyquinoline)aluminum Microcrystals with Crystallization-Induced Enhanced Electrochemiluminescence for Acetamiprid Analysis.

Improving the electrochemiluminescence (ECL) efficiency of luminophores has always been the goal of the ECL field. Herein, a novel crystallization-induced enhanced ECL (CIE ECL) strategy was exploited to significantly enhance the ECL efficiency of metal complex tris-(8-hydroxyquinoline)aluminum (Alq3). Alq3 monomers self-assembled and directionally grew to form Alq3 microcrystals (Alq3 MCs) in the presence of sodium dodecyl sulfate. The highly ordered crystal structure of Alq3 MCs not only constrained the intramolecular rotation of Alq3 monomers to decrease nonradiative transition but also accelerated the electron transfer between Alq3 MCs and coreactant tripropylamine to increase radiative transition, thus leading to a CIE ECL effect. Alq3 MCs exhibited brilliant anode ECL emission, which was 210-fold stronger than that of Alq3 monomers. The exceptional CIE ECL performance of Alq3 MCs coupled the efficient trans-cleavage activity of CRISPR/Cas12a assisted by rolling circle amplification and catalytic hairpin assembly to fabricate a CRISPR/Cas12a-mediated aptasensor for acetamiprid (ACE) detection. The limit of detection was as low as 0.79 fM. This work not only innovatively exploited a CIE ECL strategy to enhance the ECL efficiency of metal complexes but also integrated CRISPR/Cas12a with a dual amplification strategy for the ultrasensitive monitoring of pesticides such as ACE.

Novel Ratiometric Electrochemiluminescence Biosensor Based on BP-CdTe QDs with Dual Emission for Detecting MicroRNA-126.

The electrochemiluminescence (ECL) ratiometric assay is usually based on two different ECL luminophores, and the choice of two suitable luminophores and shared co-reactant makes its construction challenging. The single-emitter-based ECL ratio mode could overcome the limitation of two luminophores and simplify the construction process, so it is an ideal choice. In this work, CdTe quantum dots (CdTe QDs) were modulated using black phosphorus (BP) nanosheet to simultaneously emit the cathodic and anodic ECL signals, and H2O2 and tripropylamine (TPrA) served as the cathodic and anodic co-reactants, respectively. MicroRNA-126 (miRNA-126) was selected as the template target to exploit the application of BP-CdTe QDs in the single-emitter-based ECL ratio detection. Through the target recycling triggering rolling-circle amplification (RCA) reaction, a large amount of glucose oxidase (GOx)-modified single strand 1 was introduced. GOx catalyzed glucose to produce H2O2 in situ, which acted as a dual-role moderator to quench the anodic ECL emission with TPrA as the co-reactant while enhancing the cathodic emission, thereby realizing the ratiometric detection of miRNA-126 with a low detection limit of 29 aM (S/N = 3). The dual-ECL-emitting BP-CdTe QDs with TPrA-H2O2 as dual co-reactant provide a superior ECL ratio platform involving enzyme catalytic reaction, expanding the application of single-emitter-based ratio sensing in the diverse biological analysis.

Upconversion photoluminescence analysis of fluoroquinolones.

The characteristics of the upconversion (UC) photoluminescence (PL) of fluoroquinolones (FQs) are reported here for the first time. Using UC PL, a simple, sensitive, and cost-effective method of determining FQs was developed that eliminated interference arising from biological background fluorescence and did not require UV light to excite the FQ (in contrast to downconversion PL), which is an advantage given that UV is potentially damaging to organisms. Ciprofloxacin (CPFX) and levofloxacin (LVFX), two important FQs, were studied. The effects of acidity, temperature, the solvent used, ionic strength, and stable time on the UC PL from the two FQs were also investigated. The UC PL intensity was found to be proportional to the concentration of CPFX over the range 0.05-100 µmol/L with a correlation coefficient of 0.9992, and proportional to the concentration of LVFX over the range 0.05-100 µmol/L with a correlation coefficient of 0.9991. The limit of detection (LOD) was 6.05 nmol/L for CPFX and 5.64 nmol/L for LVFX. The proposed method was successfully used to determine FQs in human serum and pharmaceutical samples. The recoveries of the two FQs ranged from 96.0% to 103.2% and the RSD was < 2.62%. Graphical abstract.

Synthesis of the Cu-Doped Dual-Emission Fluorescent Carbon Dots and Its Analytical Application.

New Cu-doped dual-emission carbon dots (D-CDs) were synthesized rapidly and simply via a one-pot solvothermal method, and its special photoluminescence mechanism was studied. D-CDs have two fluorescence (FL) emission peaks under one-wavelength excitation and can be used as dual-signal sensor which is usually designed with two or more substances. The prepared CDs show excellent water solubility, photostability, salt tolerance, oxidation resistance, and special optical properties. The raw material ratio, solvent, pH, time, and synthesis temperature were optimized. The characterizations of CDs including transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma spectroscopic analysis, X-ray diffraction assignation of phases, thermogravimetric analysis and differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, FL spectrum, and ultraviolet-visible spectrum (UV-vis) were conducted. The investigation on mechanism indicates that the unique dual-emissive property is mainly caused by the energy-level gaps generated by the surface defects of CDs. The prepared D-CDs have good potential in dual-signal analysis and visualization sensing. To demonstrate the practical application, ferric ions, vitamin A acetate, and pH have been determined successfully.

Preparation of mesoporous silica nanoparticles molecularly imprinted polymer for efficient separation and enrichment of perfluorooctane sulfonate.

As a persistent organic pollutant, perfluorooctane sulfonate has drawn a worldwide attention. In this contribution, a novel molecularly imprinted polymer based on mesoporous silica nanoparticles was prepared for efficient separation and enrichment of perfluorooctane sulfonate in water samples. The polymer was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and N2 adsorption/desorption experiments. The static adsorption experiments and the adsorption kinetic tests were conducted. The results showed that the adsorbents had high adsorption capacity (21.10 mg/g) and short adsorption equilibration time (25 min). Meanwhile, the effect of mesoporous silica nanoparticles on the adsorption capacity was investigated. The results indicated that the mesoporous structure helped to increase the adsorption capacity of adsorbent to adsorbate. Besides, the adsorbents show good specificity and good reusability with the adsorption capacity of adsorbent toward perfluorooctane sulfonate decreasing <5% after five adsorption-desorption cycles. The mesoporous silica nanoparticles molecularly imprinted polymer has been used successfully for the removal of perfluorooctane sulfonate in environmental water samples with relative standard deviation ≤4.64%.

One-Pot Hydrothermal Synthesis of Carbon Dots with Efficient Up- and Down-Converted Photoluminescence for the Sensitive Detection of Morin in a Dual-Readout Assay.

Blue luminescent carbon dots (CDs) with a high photoluminescence (PL) quantum yield (48.3 ± 5.3%) were prepared by the one-pot hydrothermal reaction of citric acid with poly(ethylenimine) (PEI). The CDs display bright PL, narrow emission spectra, pH-dependent PL intensity, high photostability, and up-converted luminescence. The CDs exhibit a quenching of both down- and up-conversion PL in the presence of morin and thus serve as useful probes for morin detection. Both down- and up-conversion measurements allow the quantification of concentrations from 0 to 300 µmol/L with a detection limit of 0.6 µmol/L, and this dual-mode detection increases the reliability of the measurement. The proposed method of determination is simple, sensitive, and cost-effective, with potential applications in clinical and biochemical assays.

Preparation of magnetic molecularly imprinted polymers for the rapid and selective separation and enrichment of perfluorooctane sulfonate.

As a persistent organic pollutant, perfluorooctane sulfonate has drawn a great worldwide attention. In this contribution, a novel material of magnetic molecularly imprinted polymers, based on perfluorooctane sulfonate, as a template, molecule was prepared. The magnetic molecularly imprinted polymers were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometry. The adsorption isotherm was measured, and adsorption kinetic tests were conducted. The adsorbents possess high recognition ability (2.460 mg/g) and short adsorption equilibration time (60 min). Besides, they show good specificity and good reusability with the adsorption capacities of adsorbent toward perfluorooctane sulfonate decreasing less than 3% after five adsorption-desorption cycles. The magnetic molecularly imprinted polymers were used successfully in the separation and enrichment of perfluorooctane sulfonate in real water sample and exhibited good prospects in environmental treatment and monitoring.

High Sensitive and Selective Detection of PFOS with Resonance Light Scattering Technology Based on the Interaction with Victoria Blue B.

This report presents a simple, sensitive and selective victoria blue B (VBB)-based resonance light scattering (RLS) assay of perfluorooctane sulfonate (PFOS). In pH 6.0 KH2PO4-NaOH buffer solution, VBB can be protonated and reacts with PFOS through electrostatic interactions to produce ionic-association complexes. Simultaneously, the interaction leads to enhanced resonance light scattering intensities greatly, which are characterized with a peak at 277 nm. It is found that the enhanced RLS intensity is proportional to the concentration of PFOS in a range of 0.05 to 4.0 µmol·L-1. The limit of detection is 5.0 nmol·L-1. While, under the optimal experimental conditions, almost no change of the resonance light scattering intensity was observed between VBB and perfluorooctane acid (PFOA) which is one kind of representative perfluorinated compounds (PFCs). The excellent selectivity of PFOS could be due to the hydrophobicity of PFOS higher than PFOA. It is worth noting that the proposed method is capable of differentiating PFOS and some other PFCs. UV/Vis absorption spectrum and scanning electron microscope (SEM) image both were investigated to further validate the reaction mechanism. The interference of coexisting foreign substances and the optimum tests of reaction conditions, including pH value, reaction time, experimental temperature and ionic strength, were also investigated. This method has been successfully applied to the determination of PFOS in environmental water samples with RSD ≤1.74%. The experimental process as followed: In 2 mL colorimetric tube, 200 µL pH 6.0 KH2PO4-NaOH buffer solution, followed by adding 600 µL 20 µmol·L-1 VBB solution, swirl evenly, then add the right amount of PFOS solution. After vortex mixing with ultrapure water volume to 2 mL, swirl to mix, stand for 10 min at room temperature. Then the mixture was transferred for RLS measurements and absorption measurement.

Triple-wavelength overlapping resonance Rayleigh scattering method for facile and rapid assay of perfluorooctane sulfonate.

In the present study, a novel triple-wavelength overlapping resonance Rayleigh scattering (TWO-RRS) method had been well established to detect perfluorooctane sulfonate (PFOS). We found that crystal violet (CV) could react with PFOS to form 1:1 ion-association complex by electrostatic attraction and hydrophobic effect over a wide pH range (5.0∼11.0) in less than 60 s. The complexes would further self-aggregated into nanoparticles [CV-PFOS]n. Based on this phenomenon, not only the absorption and Raman spectra were changed but also the resonance Rayleigh scattering (RRS) intensities were significantly enhanced. And three new RRS peaks located at 327, 492, and 654 nm were clearly observed, respectively. At the same time, it was found that both the enhanced single-wavelength resonance Rayleigh scattering (SW-RRS) and TWO-RRS intensities against the concentration of PFOS showed an excellent correlation. The detection limits for the three single peaks were 27.4 nmol L(-1) (13.7 µg L(-1), 327 nm), 27.5 nmol L(-1) (13.8 µg L(-1), 492 nm), and 31.4 nmol L(-1) (15.7 µg L(-1), 654 nm), and for TWO-RRS method was 5.9 nmol L(-1) (3.0 µg L(-1)). Moreover, it could be applied to determine PFOS water samples successfully.

[Colorimetric assay of perfluorooctanesulfonate based on gold nanoparticles].

For the property of persistent, bioaccumulation and genetic toxicity, perfluorooctanesulfonate (PFOS) is classified as a sort of persistent organic pollutants (POPs). It is significant to develop a novel assay for the determination of PFOS. In this work, we create a new colorimetric assay for PFOS in which the positively-charged gold nanoparticles (AuNPs) work as a nano-probe. This method works on the aggregation of AuNPs induced by PFOS via electrostatic interaction. The stable monodisperse AuNPs coated by cysteamine present color of red wine and the addition of PFOS can make the monodispersed AuNPs aggregated resulting in the color change from wine red to reddish purple with a red-shift in ultraviolet-visible absorption spectrum. The experimental results show that AuNPs has a characteristic absorption peak (524 nm), as well as a wide absorption peak (650 nm) and the absorption signal intensity is proportional to the PFOS content in a range of 0. 8-8. 0 µmo .l L-1. According to these, we developed a method based on ultraviolet-visible absorption and colorimetric to detect PFOS with the detection limit of 80 nmol . L-1. The scanning electron microscope (SEM) was investigated and the photos show that the stable AuNPs are made and the degree of AuNPs aggregation is related with PFOS concentration. The effect tests of coexisting substances in system show that common anions had less impact on the system and inorganic metal ions had some interference, which can be get rid of by cat- ion exchange resin in real sample. This assay was applied to detect PFOS in tap water with a recovery range of 87. 5%-118% and RSD 4. 4%. It is a novel application of AuNPs-based probe for PFOS detection. The proposed method has more advantages such as rapidity, low-cost and simplicity than conventional ones. In addition, it has the visual sensing function and the difference of color can be sensed by naked eyes directly, which produce ideas of real-time colorimetric strategies of nanoprobe application in environmental pollutant detection.

[Gold nanoparticles-based localized surface plasmon resonance scattering analysis method for the determination of trace amounts of Hg(II)].

Heavy-metal ions pose severe risks for human health and the environment. In particular, mercury-based pollutants are of great environmental concern because of the high toxicity of many Hg compounds. It is important to monitor the levels of potentially toxic metal Hg(II) in aquatic ecosystems. Gold nanoparticles (AuNPs) as nanomaterials have been generally studied. It is because their unique electrical, chemical, optical, and catalytic properties, AuNPs have caused widespread interest for applications in biological and chemical analysis and detection. In the present work, the authors took advantage of the aggregation-induced localized surface plasmon resonance (LSPR) light scattering signal change of sodium thioglycolate functionalized AuNPs in aqueous solutions to develop a highly efficient optical sensor for Hg(II). The as-modified AuNPs demonstrate that high negative charge densities exist on their surfaces at pH 9.0 Britton-Robinson (BR) buffer solution. The AuNPs occur aggregate in solution through chelation in the presence of Hg(II). The scanning electron microscope (SEM) images for the AuNPs display typical shapes of these AuNPs as regular and almost individual spherical particles. The color change of the AuNPs solution was induced by the addition of Hg(II) and it immediately changed from red to purple due to the aggregation. Under optimum conditions, a good linear relationship was obtained from 0.08 to 0.8 µmol x L(-1) with a correlation coefficient of 0.997 6, and the limit of detection (LOD) was 8.0 nmol x L(-1). PEG20000 was employed as a system stabilizer. The proposed method has an excellent selectivity for Hg(II) in aqueous medium over other metal ions. The optimum test of reaction conditions, including the amount of AuNPs, pH value, reaction stability and ionic strength, were also investigated. This method has been used for determination of Hg(II) successfully in environmental water sample. This approach manifested several advantages including short analysis time, high sensitivity, low cost, excellent selectivity and ease of operation.

The novel up/down-conversion dual-emission carbon dots for dual-channel ratiometric fluorescence detection of pH and Cu2.

Up/down-conversion dual-emission carbon dots (U/D-CDs) are rare and have potential in analytical sensing. Herein, a kind of novel U/D-CDs was prepared successfully by a one-step solvothermal method. The prepared U/D-CDs exhibited similar dual-emission behaviors at excitation wavelengths of 300 nm and 680 nm, respectively. In addition, U/D-CDs displayed good photostability and salt-resistance. Due to the protonation-deprotonation, U/D-CDs showed strong pH dependence in the pH range of 2.0-8.0, which developed an up/down-conversion dual-channel ratiometric fluorescence (FL) probe of pH. The FL intensity of U/D-CDs can be effectively quenched by Cu2+ through the static quenching effect. Meanwhile, an obvious color change from yellow-green to blue can be observed under ultraviolet light with the increase of Cu2+ concentration. The up/down-conversion dual-channel ratiometric fluorescence sensor can be used for the visual sensing of pH and Cu2+, which also eliminates background signals and improves its accuracy and selectivity in complex samples.

One-step solvothermal synthesis of full-color fluorescent carbon dots for information encryption and anti-counterfeiting applications.

Multicolor fluorescent carbon dots (CDs) have received extensive attention due to their excellent fluorescence tunable performance. In this study, multicolor CDs with color tunable and high fluorescence quantum yields (QYs) were successfully prepared under the same conditions by a one-step solvothermal method using 2-aminoterephthalic acid (ATA) and Nile Blue A (NBA) as reaction reagents, achieving a wide color field coverage. Detailed studies on the relevant mechanisms have been carried out for blue, green and red CDs, indicating that the regulating mechanism of multicolor luminescence is determined by the size of the sp2 conjugated domains, which is due to the increase of particle size that causes an increase in the size of the sp2 conjugated domains, resulting in the narrowing of the band gap and the red-shift of the emission wavelength. It was found that the CDs have the advantages of simple preparation, high photostability and high quantum yield. They were used as fluorescent ink and mixed with polyvinyl alcohol (PVA) to form CD/PVA composites, which were successfully applied in the field of information encryption and anti-counterfeiting. This work provides a new strategy for the synthesis of panchromatic tunable fluorescent CDs and their application in the field of information encryption and anti-counterfeiting.

Dye-based dual-emission Eu-MOF synthesized by Post-modification for the sensitive ratio fluorescence visualization sensing of ClO.

As we all know, excessive hypochlorite will be transformed into highly toxic substances, while insufficient hypochlorite can not completely kill bacteria and viruses in water. Therefore, it is desirable to develop a new analytical method to detect ClO- in environmental water. Here, a novel and simple fluorescence sensor was constructed for monitoring ClO- by an effective strategy. An Acriflavine@lanthanide metal-organic framework (Acr@Eu(BTEC)) was designed by covalently integrating amino-rich dye (Acr) and carboxyl-rich Eu(BTEC) via post-synthesis method. The created fluorescence sensor has two emission centers originating from Acr and Eu(BTEC), respectively. In the presence of ClO-, the strong green fluorescence derived from Acr was significantly quenched, while the invariant red emission from Eu3+ acted as the reference signal. Thus, Acr@Eu(BTEC) with two emissions was developed as a ratiometric fluorescence sensor for highly sensitive and selective detection of ClO-. The limit of detection (LOD) was as low as 10.75 nM. Moreover, visual detection of ClO- by the naked eyes is feasible with obvious fluorescent color changes from green to orange and then red. This method shows excellent performance in practical application, which suggests that it has great potential in water quality monitoring.

Potentially tunable ratiometric electrochemiluminescence sensing based on conjugated polymer nanoparticle for organophosphorus pesticides detection.

In general, suitable double luminophores and their coreactants are necessary for constructing electrochemiluminescence (ECL) ratio strategy. However, the complexity of matching double luminophores and the stability and repeatability problem suffered by introducing exogenous coreactant would greatly limit the application of ratio detection. An original single-luminophore-based ECL ratio sensing was developed excluding any exogenous coreactants in this work. The poly [9,9-bis(3'-(N,N-dimethylamino)propyl)- 2,7-fluorene]-alt-2,7-(9,9-dioctylfluorene)] nanoparticles (PFN NPs) were explored to emit two anodic ECL signals. One centered at + 1.25 V (ECL-1) with the scanning potential of 0 ~ + 1.25 V and the other at + 1.95 V (ECL-2) with the scanning potential of 0 ~ + 1.95 V. ECL-1 showed a very strong emission without any exogenous coreactant. Importantly, hydrogen peroxide (H2O2) was able to efficiently weaken ECL-1 but strengthen ECL-2. When organophosphorus pesticides (OPs) were absent, the immobilized acetylcholinesterase-choline oxidase (AChE-ChOx) would catalyze the substrate acetylthiocholine chloride (ATCl) to produce H2O2, resulting in a quenched ECL-1 and an enhanced ECL-2. With the introduction of OPs, ECL-1 increased while ECL-2 accordingly decreased as OPs prohibited production of H2O2 by inhibiting activity of AChE. Highly sensitive ECL ratio detection for OPs was realized based on the change of the ratio of two signals. The dual anode emission properties of PFN NPs coupled with the opposite regulation of H2O2 on the two signals paved a new avenue for potentially tunable ECL ratio sensing strategy, and showed enormous potential applications for OPs analysis.

A highly sensitive dual-readout assay for perfluorinated compounds based CdTe quantum dots.

Perfluorooctanoic acid (PFOA) and Perfluorooctane sulfonate (PFOS) are two typical perfluorinated compounds (PFCs) that poss potential ecological toxicity. In this work, a fluorescence and resonance light scattering (RLS) dual-readout strategy for the detection of PFCs at picomole level based on the water-soluble CdTe quantum dots (CdTe QDs) has been proposed. It is found that the CdTe QDs exhibit a quenching in the presence of PFCs and thus serve as useful probes for PFCs. The linear ranges are 0.032-10.0 nM with a limit of detection(LOD) of 32.02 pM for PFOA and 0.044-15.0 nM with a LOD of 43.96 pM for PFOS, respectively. Meanwhile, PFCs can form complexes with CdTe QDs in acid medium, resulting in remarkable RLS signals. The enhanced RLS intensities are in proportion to the concentrations of PFOA and PFOS, respectively. And the linear ranges are 0.048-5.0 nM with a LOD of 47.78 pM for PFOA, and 0.057-5.0 nM with a LOD of 56.72 pM for PFOS, respectively. This dual-mode detection increases the reliability of the measurement. The proposed method is simple, sensitive and cost-effective, with potential applications in environmental monitoring and assessment.

One-pot hydrothermal synthesis of Si-doped carbon quantum dots with up-conversion fluorescence as fluorescent probes for dual-readout detection of berberine hydrochloride.

Here, the high fluorescent silicon-doped carbon quantum dots (Si-CQDs) were prepared by a facile and one-pot hydrothermal assay using 3-aminopropyltrimethoxysilane as the carbon and silicon source. The prepared Si-CQDs exhibit favorable water-soluble, high-temperature resistance, acid resistance, alkali resistance, high ionic strength resistance, high photostability, film-forming ability and solid-state fluorescence. Compared to other Si-CQDs that have been reported, the prepared Si-CQDs show unique up-conversion fluorescence. Furthermore, it is found that berberine hydrochloride (BH) can effectively quench the down- and up-conversion fluorescence of the Si-CQDs, making it can be used as a highly sensitive and specific probe for BH dual-mode sensing. Meanwhile, the linear range of down-conversion fluorescence detection for BH is 0.5-30.0 µmol/L with a limit of detection (LOD) of 50 nmol/L, and the linear range of up-conversion fluorescence assay for BH is 0-25.0 µmol/L. The mechanism of down-conversion fluorescence quenching by BH was investigated through a series of studies. The results show the quenching mechanism is the inner filter effect (IFE). Moreover, this proposed strategy has been well used to analyze BH in urine samples with satisfactory results.

Strategy to Synthesize Tunable Multiemission Carbon Dots and Their Multicolor Visualization Application.

Studies on multiemission fluorescent carbon dots (CDs) excited at one wavelength are extremely promising because of their label-free property, facile synthesis, multicolor visualization, and prevention of background interference. In this study, a novel template strategy to develop multiemission carbon dots (M-CDs) using fluorescent precursors has emerged. We attempted to elucidate the relationship between precursor substances and luminescence origins. The M-CDs prepared by calcein demonstrate three emissions, ultraviolet (UV), blue, and green, which are attributed to the solvent, surface defect, and precursor aromatic ring luminophores, respectively. Also, through a regular adjustment of the amount of NaOH or the solvothermal synthesis time, the expected optical requirements were successfully met by the M-CDs, which is a better capability than that of previously reported M-CDs. In addition, a multicolor sensor designed with M-CDs and rhodamine B (RhB) has been successfully applied in cell imaging. When exposed to different pH media, the fluorescence (FL) emission shows a linear relationship with the pH value, displaying a profuse color evolution from dark blue to light blue, cyan, green, yellow, and finally, orange.

A design strategy of dual-ratiomentric optical probe based on europium-doped carbon dots for colorimetric and fluorescent visual detection of anthrax biomarker.

In this work, a novel dual-ratiometric optical probe based on europium-doped carbon dots (Eu-CDs) was developed for colorimetric and fluorescent visual sensing dipicolinic acid (DPA), a anthrax biomarker. Eu-CDs with recessive signals were prepared via thermal pyrolysis method. And the magenta appears when Eu-CDs coordinates with Eriochrome Black T (EBT). Based on the ligand displacement strategy, DPA reduces magenta and makes blue appear, which develop ratiometric colorimetric visual detection methods of DPA. Under 270 nm excitation, DPA make the red fluorescence signal of Eu in EBT-CDs@Eu appear, based on the absorbance-energy transfer-emission effect, the ratiometric fluorescent visual detection assay of DPA has been developed. Based above, dual-ratiometric optical probe was designed successfully. The limit of detection (LOD) is 10.6 nM for ratio colorimetric assay. More prominently, naked-eye determination of DPA without instrument is as low as 1.0 µM. Furthermore, its practicability was verified by quantifying the DPA in Bacillus subtilis spores and human urine (with RSD≤2.35%). The sensor shows great superiority in on-site analysis of DPA, especially in limited instruments conditions.

A new dual-recognition strategy for hybrid ratiometric and ratiometric sensing perfluorooctane sulfonic acid based on high fluorescent carbon dots with ethidium bromide.

In this work, a novel strategy for perfluorooctane sulfonic acid (PFOS) detection was established by using a ratiometric nanosensor with the combination of fluorescence and second-order scattering (SOS). The practical ratiometric nanosensor was synthesized simply by mixing fluorescent dye ethidium bromide (EB) and nitrogen doped carbon dots (N-CDs) which was synthesized by a one-step hydrothermal method with Victoria Blue B, possessing three emission peaks at 472 nm, 560 nm and 600 nm under a single wavelength excitation of 280 nm, respectively. The EB served as the reference signal label, and the N-CDs, having response to the analytes, acted as the response signal label. To achieve ratiometric detection, the fluorescence emission of the N-CDs was turned off and the SOS emission was turned on with the addition of the target PFOS. To achieve colorimetric detection, with the help of EB, the fluorescence of the system changed from green to orange. Under the optimal conditions, the difference of F472/I568 of the nanosensor had good linearity against the concentrations of PFOS within a linear range of 0-2.0 µM. The limit of detection was as low as 27.8 nM, which was low enough for the detection of PFOS in water samples. The proposed method has been successfully applied to the detection of PFOS with RSD <1.67%. The results show that the as-prepared N-CDs/EB ratiometric nanosensor has potential application for the detection of PFOS in environmental monitoring.