Highly Sensitive ß-Lactoglobulin Fluorescent Aptamer Biosensors Based on Tungsten Disulfide Nanosheets and DNase I-Assisted Signal Amplification.

ß-lactoglobulin (ß-Lg) is a protein found in milk that can cause severe allergic reactions, including rash, vomiting, and diarrhea. Thus, it is crucial to develop a sensitive ß-Lg detection method to protect people who are susceptible to allergies. Here, we introduce a novel and highly sensitive fluorescent aptamer biosensor for detecting ß-Lg. First, a fluorescein-based dye (FAM)-labeled ß-lactoglobulin aptamer (ß-Lg aptamer) is adsorbed on the surface of tungsten disulfide (WS2) nanosheets via van der Waals forces, resulting in fluorescence quenching. When ß-Lg is present, the ß-Lg aptamer selectively binds to ß-Lg, causing a conformational change in the ß-Lg aptamer and releasing it from the surface of WS2 nanosheets, which restores the fluorescence signal. Simultaneously, DNase I in the system cleaves the aptamer bound to the target, producing a short oligonucleotide fragment and releasing ß-Lg. The released ß-Lg then binds to another ß-Lg aptamer adsorbed on WS2, initiating the next round of cleavage, resulting in significant amplification of the fluorescence signal. This method has a linear detection range of 1-100 ng mL-1, and the limit of detection is 0.344 ng mL-1. Furthermore, this approach has been successfully used for detecting ß-Lg in milk samples with satisfactory results, providing new opportunities for food analysis and quality control.

Fluorimetric identification of sulfonamides by carbon dots embedded photonic crystal molecularly imprinted sensor array.

Identification of sulfonamides (SAs) residues in food is vital for human health. A set of 4-channel sensor array was constructed by carbon dots (CDs) embedded in photonic crystal molecularly imprinted (PCMIP@CDs) film which included 3 PCMIP@CDs units and 1 PCNIP@CDs unit to determine typical SAs: sulfadimethoxine, sulfathiazole, sulfaguanidine, sulfamethazine, sulfadiazine. Under the optimal conditions, the response time of the sensor array was only 200 s. Moreover, 300 fluorescence response signals (4 sensor units × 5 sulfonamides × 3 concentrations × 5 repeats) were processed by pattern recognition technique to analyze the ability of the sensor array to recognize 5 kinds of SAs. Subsequently, the linear discrimination analysis (LDA) method was used to identify the five SAs simultaneously with 100 % classification accuracy and the limit of detection was 0.01-0.26 nmol/L. Moreover, the proposed method can effectively identify-five SAs in water and fish samples.

Long-distance mobilization of chromium(III) in soil associated with submicron Cr2O3.

Trivalent chromium is generally assumed to form insoluble species, resulting in low mobility of Cr(III) in soils. Here, we report continuous distributions (0-19 m) of a high concentration of Cr(III) in the alkaline soils of a historically industrial site for producing Na2Cr2O7, CrO3, and Cr2O3, which challenges this abovementioned conventional wisdom. The thermodynamic equilibrium model showed the low possibility of Cr(III) originating from Cr(VI) reduction under the redox conditions of this study. The AF4-MALLS-ICP-MS and µ-XRF-XANES were used to identify the particle size distribution of Cr(III)-containing colloids and Cr(III) species in mobile colloids. In any soil layer, Cr(III) accounts for 71.1-94.3% of the total Cr in submicron soil colloids and is composed of submicron intrinsic Cr2O3 (55.2%-63.8%), Cr(OH)3 (0-33.0%), and Cr(III) adsorbed by ferrihydrite (0-19.0%) and clay montmorillonite (11.1%-21.1%) colloid. On the contrary, Cr(VI) was mainly distributed in bulk soil (> 2 µm) except for the topsoil, accounting for 62.6-90.0% of total Cr(VI). Organic matter content and soil texture are the most critical factors driving the mobilization of submicron colloids in soils by principal component analysis. Humic acid (HA) formed HA-corona on Cr2O3 surface and enhanced colloidal dispersion, thereby accelerating the long-distance mobilization of submicron Cr2O3 colloids in alkaline soil layers, whereas the heteroaggregation of clay colloid with Cr2O3 was only favorable for short-distance mobilization. Our findings help to re-recognize the potential migration risks of insoluble heavy metals in soils.

Sensitive and multicolor detection of nitrite based on iodide-mediated etching of gold nanostars.

Excessive intake of nitrite is a serious risk to human health. Research on the method of detecting nitrite in food is of great significance to avoid this issue. In this work, we report a colorimetric method based on iodide-mediated etching of gold nanostars (Au NSs) for the determination of nitrite with high selectivity and sensitivity. In the presence of iodide, the strong affinity between iodide and Au NSs results in the rapid etching of Au NSs into spherical gold nanoparticles, resulting in significant changes in the surface plasmon resonance (SPR) spectrum and the solution color. Because nitrite can oxidize iodide under acidic conditions, the etching degree of Au NSs could be controlled by adding different nitrite concentrations to consume iodide, leading to quantitative detection of nitrite. Under the optimal conditions, nitrite exhibits a good linear relationship with the absorption ratio (A820 nm/A570 nm) in the concentration range of 2-300 µM, with a detection limit of 0.4 µM. The as-proposed method was successfully applied to determination of nitrite in cabbage and sausage, and the results showed good reproducibility and accuracy.

Fluorescence detection of milk allergen ß-lactoglobulin based on aptamers and WS2 nanosheets.

ß-Lactoglobulin (ß-Lg), a food allergen, can easily cause allergic reactions in infants and young children. Therefore, it is necessary to develop a rapid, sensitive, and selective detection method to protect individuals prone to allergies. In this paper, a fluorescence assay based on WS2 nanosheets and a fluorescent dye (FAM)-labeled ß-Lg aptamer was designed to detect ß-Lg rapidly with high sensitivity. In the sensing platform, the ß-Lg aptamer is adsorbed on the WS2 nanosheet surface by van der Waals forces, which trigger the phenomenon of fluorescence resonance energy transfer (FRET) and suppress the fluorescence signal in the system. When ß-Lg is present, the conformation of the aptamer specifically bound to ß-Lg changes. Therefore, the aptamer is separated from the WS2 nanosheet surface, and the fluorescence signal is recovered. This method combines the high quenching efficiency of WS2 nanosheets and good specificity of the ß-Lg aptamer. The detection range of this method for ß-Lg is 0.1-100 µg mL-1. The detection limit is 20.4 ng mL-1. This method exhibits high sensitivity, selectivity and good reproducibility, and it can be used for ß-Lg detection in actual samples.

A sensitive colorimetric hydrogen sulfide detection approach based on copper-metal-organic frameworks and a smartphone.

In this study, we demonstrate a colorimetric approach for the detection of hydrogen sulfide (H2S) in water samples with high sensitivity. Firstly, copper-metal-organic frameworks (Cu-MOFs) were synthesized by ultrasonic-assisted hydrothermal method, presenting a maximum absorption peak at 700 nm. It was found that Cu-MOFs could react with H2S to form a copper-sulfur complex along with a decrease of the absorption peak at 700 nm and a visible color change from blue to tan. Under the optimal reaction conditions, the absorption intensity at 700 nm was linear with H2S concentration in a range of 0.05-2 mM (R2 = 0.9928), providing a detection limit of 22 µM. Furthermore, the method was successfully applied to the detection of H2S in lake water samples with a recovery rate between 94.4% and 112.6%. In addition, a practical and portable device for on-site H2S detection was designed by using agarose hydrogels, and a simple colorimetric detection method based on a smartphone was developed. This analytical method showed good selectivity for H2S compared to other interfering substances, and the feasibility of the agarose hydrogel-based device was proved by the determination of H2S in real lake water samples.

Effectiveness and mechanism for the simultaneous adsorption of Pb(II), Cd(II) and As(III) by animal-derived biochar/ferrihydrite composite.

The emerging animal-derived biochar (AB) has shown potential for mitigating the contamination of cationic heavy metals, but has no affinity to oxyanionic metals. In this study, we developed an AB/ferrihydrite composite with a AB/Fe mass ratio of 4.0 (ABF-4) for the simultaneous adsorption of cationic Pb(II)/Cd(II) and anionic As(III). ABF-4 is a type of hydroxyapatite-rich biochar coated with nanoscale iron hydroxide aggregates. The adsorption of Pb(II), Cd(II), and As(III) on ABF-4 were 2.64, 1.55, and 0.48 mmol/g, and were 135%, 150%, and 4500% higher than those of pure AB, respectively. The enhanced adsorption of Pb(II) and Cd(II) by ABF-4 is partially due to the increase in surface area and micropores. The nano-sized ferrihydrite on ABF might help form surface complexation with As(III) and oxidize As(III) to As(V). In multimetal systems, Pb(II) and Cd(II) can promote As(III) adsorption due to the formation of NaPb4(AsO4)3 precipitate and the ternary complex of arsenite and cadmium with ABF-4, whereas Cd(II) adsorption might be inhibited because of the surface coverage of Pb5(PO4)3Cl precipitate on ABF-4. However, the coexistence of Pb in soils does not influence the immobilization of Cd. The amendment of ABF-4 can considerably decrease the availability of Pb, Cd, and As in soils from Pb-Zn smelting sites. Hence, ABF-4 is a promising multifunctional material for the potential immobilization of multicomponent heavy metals.

Pb(II)-mediated precipitate transformation promotes Cr(VI) immobilization by biogenic hydroxyapatite.

In this work, the mechanism of Pb(II)-mediated precipitation transformation to improve the removal of Cr(VI)-oxyanion on biogenic hydroxyapatite (BHAp) were investigated. The Pb(II)-preloading formed pyromorphite [Pb5(PO4)3Cl] precipitate on the BHAp surface (Pb@BHAp), thus causing an increase of 2.2 times in the uptake of Cr(VI) by Pb@BHAp at pH of 2.4. It was primarily due to the dissolution of Pb5(PO4)3Cl accompanied with the release of Pb(II), resulting in the rapid formation of crocoite (PbCrO4). Although the Ksp of Pb5(PO4)3Cl was approximately 23 orders of magnitude lower than that of PbCrO4, Pb(II)-mediated precipitation transformation could still occur. XRD and SEM-EDX analyses demonstrated that the process was a time-dependent that included rapid crystal precipitation in the initial 10 min and subsequent precipitate accumulation for several hours. The Pb(II) released from the dissolution of Pb5(PO4)3Cl was immediately immobilized by Cr(VI); therefore, it did not cause any retention risk of Pb(II) in the solution. Furthermore, a small quantity of Cr(VI) could be reduced to Cr(III) by BHAp, and Cr(III) could enter into the BHAp lattice for the exchange of Ca(II). This study provides a new insight into the resource utilization of Pb-bearing BHAp and a potential method for the successive removal of Pb(II) and Cr(VI).

Aptamer-Pendant DNA Tetrahedron Nanostructure Probe for Ultrasensitive Detection of Tetracycline by Coupling Target-Triggered Rolling Circle Amplification.

Tetracycline (TET) is a broad-spectrum antibiotic, which is frequently used in the prevention and treatment of animal diseases, feed additives, and so on. However, its residue and accumulation in animal-derived foods could cause several side effects to the human body. Herein, we fabricated TET aptamer-pendant DNA tetrahedral nanostructure-functionalized magnetic beads (Apt-tet MBs) as a probe to detect TET. In the presence of target TET, DNA primer was released from Apt-tet MBs since the TET aptamer could specifically bind TET. Next, the separated DNA primer could effectively initiate rolling circle amplification (RCA) reaction and generate a long tandem single-stranded sequence. Finally, with SYBR Green I as the fluorescence dye, the fluorescence signal could be detected by detection probes through hybridizing the RCA product. Under optimal conditions, the fluorescent signal increased with the increasing target TET concentration within the 5 orders of magnitude dynamic range from 0.001 to 10 ng mL-1. The detection limit was calculated to be 0.724 pg mL-1 and the method showed high selectivity toward TET among different antibiotics. More impressively, this method was employed for TET determination in fish and honey samples. The as-obtained results were consistent with those of ELISA kits, holding great potential in the field of food analysis.

Histamine detection in fish samples based on indirect competitive ELISA method using iron-cobalt co-doped carbon dots labeled histamine antibody.

Due to complex matrixes and specific reagent deficiency, the rapid detection of histamine is still a challenge to date. Based on the high peroxidase-like activity of iron-cobalt co-doped carbon dots, an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was established for histamine detection using the mimic enzyme labeled with histamine antibody (His-Ab). Through the competitive binding of the labeled His-Ab to solid-phase and sample antigens, histamine content was detected with a linear range of 2.5-150 µg mL-1. The detection limit based on 3σ/K was 0.50 mg kg-1, which was much lower than those of commercial His-kit and HPLC methods. The ic-ELISA method was applied to histamine detection in fish samples with the recovery of (103.4 ± 0.5)%, which was in accord with those of commercial His-kit and HPLC methods. The results indicated that the established ic-ELISA method was suitable for rapid detection of histamine in fish samples with high accuracy, sensitivity and stability.

On-Site Colorimetric Detection of Cholesterol Based on Polypyrrole Nanoparticles.

Herein, we report a facile method for cholesterol detection by coupling the peroxidase-like activity of polypyrrole nanoparticles (PPy NPs) and cholesterol oxidase (ChOx). ChOx can catalyze the oxidation of cholesterol to produce H2O2. Subsequently, PPy NPs, as a nanozyme, induce the reaction between H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB). Under optimal conditions, the increase is proportional to cholesterol with concentrations from 10 to 800 µM in absorbance of TMB at 652 nm. The linear range for cholesterol is 10-100 µM, with a detection limit of 3.5 µM. This reported method is successfully employed for detection of cholesterol in human serum. The recovery percentage is ranged within 96-106.9%. Furthermore, we designed a facile and simple portable assay kit using the proposed system, realizing the on-site semiquantitative and visual detection of cholesterol in human serum. The cholesterol content detected from the portable assay kit were closely matching those obtained results from solution-based assays, thereby holding great potential in clinical diagnosis and health management.

Aptamer-based fluorometric determination of chloramphenicol by controlling the activity of hemin as a peroxidase mimetic.

A method for the aptamer-based determination of chloramphenicol (CAP) was developed by exploiting the peroxidase mimicking activity of hemin. The method includes two hemin-modified DNA probes termed P1 and P2. P1, which was modified at its 5' end with one hemin monomer, contains the CAP-binding sequence. The hybridization between P1 and P2 brings the two hemin monomers in close proximity, resulting in the formation of a hemin dimer with low peroxidase mimicking activity. The duplex structure was dehybridized in the presence of CAP. The formed hemin monomer featured a strong peroxidase mimicking activity and catalyzed the conversion of non-fluorescent tyramine into fluorescent dityramine by hydrogen peroxide. Fluorescence (with an excitation/emission maxima at 320 and 410 nm, respectively) increased linearly in the 0.1 ng mL-1 to 10 ng mL-1 CAP concentration range. The detection limit based on the 3σ/k criterion reached 0.07 ng mL-1. The proposed assay was successfully employed for CAP detection in (spiked) honey samples with recoveries of 94.3-117.2%. Given its high sensitivity and good stability, this method shows potential in providing a platform for antibiotic detection.

Sensitive and on-site detection of glyphosate based on papain-stabilized fluorescent gold nanoclusters.

Organophosphorus pesticides can prevent or eliminate various pathogenic bacteria, insects, and weeds, and thus they are widely applied in agricultural production. However, illegal use and issues with organophosphorus pesticide residues contribute to global environmental pollution and pose a threat to public health safety. In this study, we developed a sensitive glyphosate (Glyp) fluorescence detection method using papain-stabilized gold nanoclusters (papain-AuNCs) as the fluorescence probe and a tyrosinase (TYR)/dopamine (DA) fluorescence-quenching system. The TYR catalyzed the oxidized conversion of DA into DA chrome, which served as an electron acceptor to quench the fluorescence of papain-AuNCs. However, Glyp inhibited the activity of TYR, thereby preventing DA oxidization and leading to the fluorescence recovery of papain-AuNCs. Under the optimum conditions, the fluorescence intensities of papain-AuNCs exhibited a good linear relationship with the concentration of Glyp in the range of 0.04-0.4 ng·mL-1, and the limit of detection for Glyp was 0.035 ng·mL-1. Furthermore, a paper-based sensor was constructed using the proposed system, which enabled on-site visual and semiquantitative detection of Glyp residues in tap-water samples. Overall, our strategy provides new opportunities for detection of organophosphorus pesticides and evaluation of environmental security. Graphical abstract.

Highly sensitive detection of multiple antibiotics based on DNA tetrahedron nanostructure-functionalized magnetic beads.

Functional DNAs-functionalized magnetic beads (MBs) offer great potential in bioanalysis field because of their target recognition and magnetic separation functions. However, the recognition capability and hybridization affinity of DNA probes often suffer from limited available space, poor probe conformation and non-selective adsorption. To overcome these limitations, we herein used aptamer-pendant DNA tetrahedron nanostructure-functionalized MBs (TETapt-tet MBs) to develop a target-response fluorescence method with tetracycline (TET) as a model. In the absence of TET, 6-carboxy-X-rhodamine-labeled complementary DNAs (ROX-cDNAs) were assembled on the surface of MBs. Upon the addition of target TET, the ROX-cDNAs were separated and released from the MBs to generate fluorescence signal. The limit of detection and limit of quantification for TET were found to be 6 pg mL-1 and 20 pg mL-1, respectively. Compared with ssDNA-functionalized MBs surface, the designed DNA tetrahedron nanostructure-based surface could decrease the hybridization time and reduce false positives, ensuring the accuracy of TET detection in complex samples. The presented method was successfully employed for TET detection in honey samples. Moreover, this functionalization strategy could be extended to detect multiple antibiotics by simply substituting different aptamer sequences. Therefore, the proposed method has great potential in the field of food safety and public health.

Lead competition alters the zinc adsorption mechanism on animal-derived biochar.

In this study, the adsorption behaviors and mechanisms of Pb(II) and Zn(II) by animal-derived biochar (ADB) in single and binary metal systems were comparatively investigated. ADB contains considerable amounts of Ca/P components and is mainly composed of hydroxyapatite (HAP), which plays an important role in the adsorption of Pb(II) and Zn(II). The maximum adsorption capacities of Pb(II) and Zn(II) on ADB were in the order of Zn(II)-single (3.23 mmol g-1) > Pb(II)-single (2.74 mmol g-1) ≈ Pb(II)-binary (2.71 mmol g-1) > Zn(II)-binary (2.31 mmol g-1). In the single metal system, approximately 99.9% of the adsorbed Pb(II) existed as Pb5(PO4)3Cl, while the dominant adsorption mechanism of Zn(II) was cation exchange, followed by precipitation, accounting for 78.0%-80.6% and 19.4%-21.5% of the adsorption capacity, respectively. These findings were verified by X-ray diffraction refinement, X-ray photoelectron spectroscopy, metal speciation modeling, and Ca(II) exchange experiment. In the binary metal system, the proportion and form of Pb(II) precipitate remained unchanged. However, the binding of Zn(II) to ADB was completely dependent on the cation exchange with Ca(II), and no remarkable Zn(II) precipitation was observed. Phosphate released from HAP preferentially precipitated with Pb(II) than with Zn(II) when they coexisted. Consequently, Pb(II) competition may alter the Zn(II) adsorption mechanism on ADB. Nonetheless, ADB could serve as an efficient biochar for the simultaneous immobilization of Pb(II) and Zn(II) via different mechanisms.

A dichromatic label-free aptasensor for sulfadimethoxine detection in fish and water based on AuNPs color and fluorescent dyeing of double-stranded DNA with SYBR Green I.

A dichromatic label-free aptasensor was described for sulfadimethoxine (SDM) detection. Compared with the binding of SDM-aptamer to SDM, the higher affinity of aptamer to cDNA may result in the hybridization of dsDNA. In the presence of SDM, the aptamer specifically binds to SDM, leading to a blue color of AuNPs in deposit and fluorescence at 530 nm in supernatant after adding cDNA and SGI. With no target of SDM, AuNPs protected with the aptamer re-disperse in PBS with a red color, and no fluorescence occurs in supernatant. Based on the principle, SDM can be quantitatively detected through both fluorescent emission and AuNPs color changes with recoveries ranging from 99.2% to 102.0% for fish and from 99.5% to 100.5% for water samples. An analytical linear range of 2-300 ng mL-1 was achieved with the detection limits of 3.41 ng mL-1 for water and 4.41 ng g-1 for fish samples (3σ, n = 9).

Mechanistic insights and multiple characterizations of cadmium binding to animal-derived biochar.

Cattle-derived biochar (CB), which is derived from industrial pyrolysis of cattle carcasses in harmless treatment plants, is a naturally occurring mineral form of carbonate-bearing hydroxyapatite (CHAP) with a small amount of elemental carbon. CB has 4.02% of carbonate content, which falls under the B-type substitution of CHAP. In this work, the Cd(II) sorption capacity of CB was determined to be 0.82 mmol/g, with 97.6% of the Cd(II) uptake contributing to CHAP and only 2.36% of the Cd(II) uptake contributing to the elemental carbon component. The calculation and linear combination fitting (LCF) of Cd L3-edge X-ray absorption near-edge structure (XANES) analysis indicated that the contributions of Cd(II) species to CB presented the following order: ion exchange (57.6%-61.0%) > precipitation (24.4%-29.9%) > surface complexation (12.5%-13.4%). The depth dependent X-ray photoelectron spectroscopy (XPS) showed the presence of ion exchange, which is accompanied by intraparticle diffusion. LCF of XANES and Rietveld analysis of X-ray diffraction (XRD) demonstrated that Cd(II) was precipitated in the form of Cd5H2(PO4)4·4H2O on the CB surface. Furthermore, the precipitate was directly observed and identified by scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). Consequently, we revealed the intricate binding mechanism of Cd(II) to CHAP-rich CB and confirmed the importance of surface precipitation.

Detection of Malachite Green using a colorimetric aptasensor based on the inhibition of the peroxidase-like activity of gold nanoparticles by cetyltrimethylammonium ions.

A specific and sensitive colorimetric aptasensor is described for the determination of Malachite Green (MG). It is exploiting the inhibition of the peroxidase-like activity of gold nanoparticles (AuNPs). The AuNPs act as enzyme mimics that catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to yield a dark blue solution. The catalytic activity is inhibited by hexadecyl trimethyl ammonium ion, specifically by cetyltrimethylammonium bromide (CTAB), which causes the aggregation of AuNPs. If a (negatively charged) RNA-aptamer against MG is added, it binds to the positively charged CTAB and prevents aggregation. This enhances the enzyme mimicking activity of the AuNPs and leads to the formation of a dark blue solution. However, in the presence of MG, the aptamer binds to MG, and leads to the aggregation of AuNPs again. The aggregated AuNPs possess a light blue color. A colorimetric method (best performed at 650 nm) was work out that can detect MG in a concentration range from 10 to 500 nmol L-1. The detection limit based on 3σ/k criterion is 1.8 nmol L-1. The assay is highly specific and accurate. Recoveries from spiked real samples (aquaculture water) ranged from 80% to 120%. Graphical abstract Based on the inhibition of cetyltrimethyal ammonium ion and the enhancement of RNA-aptamer, the differences of the peroxidase-like activities of AuNPs can be greatly enlarged with and without MG, by which a colorimetric aptasensor can be constructed for the detection of Malachite Green (MG).

Label-Free Fluorescence-Based Aptasensor for the Detection of Sulfadimethoxine in Water and Fish.

Fluorescence-based aptasensors possess high sensitivity but are complicated and usually require multistep labeling and modification in method design, which severely limit the practical applications. Here, a label-free fluorescence-based aptasensor, consisting of aptamer, gold nanoparticles (AuNPs), and cadmium telluride (CdTe) quantum dots (QDs), was developed for the detection of sulfadimethoxine (SDM) in water and fish based on the specific recognition of SDM-aptamer and the inner filter effect of QDs and AuNPs. In the absence of a target, AuNPs dispersed in salt solution because of the aptamer protection, which could effectively quench the fluorescence emission of QDs, while in the presence of SDM, AuNPs aggregated due to the specific recognition of SDM-aptamer to SDM, which resulted in fluorescence recovery. A linear response of SDM concentrations in the range of 10-250 ng mL-1 ( R2 = 0.99) was obtained, and the detection limit was 1.54 ng mL-1 (3σ, n = 9), far below the maximum residue limit (100 ng mL-1) of SDM in edible animal tissues regulated by China and the European Commission. The fluorescence-based aptasensor was applied to the detection of SDM in aquaculture water and fish samples with high accuracy, excellent precision, and ideal selectivity. The results indicated that the developed aptasensor was simple in design, easy to operate, and could be used to detect rapidly and accurately SDM in water and fish samples.

Ratiometric fluorescence probe of MIPs@CdTe QDs for trace malachite green detection in fish.

A facile and practical ratiometric fluorescence probe based on two CdTe quantum dots (QDs) coated with molecularly imprinted polymers (MIPs) was prepared for the detection of trace malachite green (MG) in fish. Two CdTe QDs coated with MIPs were fabricated by a one-pot method using MG, (3-aminopropyl) triethoxysilane (APTES) and tetraethyl orthosilicate (TEOS) as template, functional monomer, and cross-linker, respectively. CdTe QDs with λem 530 nm (gQDs) and 630 nm (rQDs) were used as the referential fluorophore and target sensitive fluorophore, respectively. The fluorescence intensity of gQDs remained unchanged in the presence of MG, while the fluorescence of rQDs could be quantitatively quenched by MG based on the strategy of fluorescence resonance energy transfer. The ratiometric fluorescence probe (MIPs@gQDs&rQDs) was characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The linear range of MG detection was 0.1-32 µmol L-1 with a detection limit of 8.8 µg kg-1. The constructed probe has been successfully applied to the detection of MG in fish with the recoveries of 92.3-109.1%, which were validated by the method of HPLC. The result indicated that the probe possessed rapid response, wide linear range, high sensitivity, and relatively high selectivity, and was low-cost and easy in operation in the detection of MG in fish samples.