Sensitive Fluorescence Detection Research Articles

Cascading oxidoreductases-like nanozymes for high selective and sensitive fluorescent detection of ascorbic acid

Cascading oxidoreductases-like nanozymes for high selective and sensitive fluorescent detection of ascorbic acid

Hollow Cu/CoS2 Nanozyme with Defect-Induced Enzymatic Catalytic Sites and Binding Pockets for Highly Sensitive Fluorescence Detection of Alkaline Phosphatase.

Along with an ever-deepening understanding of the catalytic principle of natural enzymes, the rational design of high-activity biomimetic nanozymes has become a hot topic in current research. Inspired by the active centers of natural enzymes consisting of catalytic sites and binding pockets, a Cu-doped CoS2 hollow nanocube (Cu/CoS2 HNCs) nanozyme integrating substitution defects and vacancies is developed through a defect engineering strategy. It is shown that the vacancies and substitution defects in the developed Cu/CoS2 HNC nanozymes serve as binding pockets and catalytic sites, respectively. The construction of this key active center and the accelerated electron transfer from the Co/Cu redox cycle significantly improve the substrate affinity and catalytic efficiency of the Cu/CoS2 HNCs nanozymes, which results in the excellent catalytic performance of the Cu/CoS2 HNC nanozymes. Using the superior enzymatic activity of Cu/CoS2 HNCs, a fluorescence detection platform for alkaline phosphatase (ALP) is established, which is a wider detection range and lower limit of detection (LOD) than previous work. This work broadens the family of nanozymes and provide a new idea for the development of novel nanozymes with high enzyme activity, as well as a guideline for the construction of highly sensitive fluorescent sensors.

A New HPLC-Fluorescence Method for the Simultaneous Determination of Fluticasone Propionate and Salmeterol Xinafoate in Their Solutions Involving Schiff-Base Derivatization with Hydrazine

A partially validated high-performance liquid chromatographic method with UV and fluorescence detection was developed to determine fluticasone propionate (FP) and salmeterol xinafoate (SX) simultaneously in their solutions. RP-HPLC (Hypersil C18 column, 250 mm × 4.6 mm, 5 µm) was used for chromatographic separation employing an isocratic mobile phase consisting of methanol, acetonitrile and water (50/20/30, v/v/v) at a flow rate of 0.8 mL.min–1. With the aid of the Schiff-base reaction, the hydrazine derivative of FP was prepared to enhance the fluorescence signal of FP. The method was employed at an excitation maximum of λ = 246, 262 and 298 nm for FP, SX and FP derivatives, respectively. The method is accurate, precise and linear (R2 ≥ 0.999) in the range of 0.246–86.957 µg×mL–1 for FP in its derivatives mixture and 0.156–50.00 µg×mL–1 for SX. The calculated LOD values are 0.081 and 0.052 µg×mL–1, respectively. It was noted that the fluorescence detection sensitivity of FP and SX is better than that of UV (LOD = 0.396 and 0.254 µg×mL–1 for FP and SX, respectively). The advantage of the validated HPLC-Fluorescence method compared with expensive and sophisticated LC-MS methods is its simplicity. When compared with other HPLC-UV/Fluorescence methods, the proposed method includes simple chromatographic conditions (no column oven nor high flow rate) and uses non-buffered mobile phase solvents; it is the first HPLC-Fluorescence method for the simultaneous determination of SX and FP. Moreover, the Fluorescence signal of FP was enhanced by derivatization with hydrazine. This was confirmed by computational and Mass spectrometric analysis.

A fluorescent aptasensor for enzyme-free and sensitive detection of kanamycin based on entropy-driven strand displacement reaction

BackgroundKanamycin is an antibiotic that can easily cause adverse side effects if used improperly. Due to the extremely low concentrations of kanamycin in food, quantitative detection of kanamycin becomes a challenge. As one of the DNA self-assembly strategies, entropy-driven strand displacement reaction (EDSDR) does not require enzymes or hairpins to participate in the reaction, which greatly reduces the instability of detection results. Therefore, it is a very beneficial attempt to construct a highly sensitive and specific fluorescence detection method based on EDSDR that can detect kanamycin easily and quickly while ensuring that the results are effective and stable. ResultsWe created an enzyme-free fluorescent aptamer sensor with high specificity and sensitivity for detecting kanamycin in milk by taking advantage of EDSDR and the high specific binding between the target and its aptamer. The specific binding can result in the release of the promoter chain, which then sets off the pre-planned EDSDR cycle. Fluorescent label modification on DNA combined with the fluorescence quenching-recovery mechanism gives the sensor impressive fluorescence response capabilities. The research results showed that within the concentration range of 0.1 nM–50 nM, there was a good relationship between the fluorescence intensity of the solution and the concentration of kanamycin. Specificity experiments and actual sample detection experiments confirmed that the biosensor could achieve highly sensitive and specific detection of trace amounts of kanamycin in food, with a detection limit of 0.053 nM (S/N = 3). SignificanceTo our knowledge, this is the first strategy to combine EDSDR with fluorescence to detect kanamycin in food. Accurate results can be obtained in as little as 90 min with no enzymes or hairpins involved in the reaction. Furthermore, our enzyme-free biosensing method is straightforward, highly sensitive, and extremely specific. It has many possible applications, including monitoring antibiotic residues and food safety.

Label-free and sensitive fluorescent detection of Escherichia coli O157: H7 in milk based on cascade strand displacement amplification and G-quadruplex-thioflavin T

The development of a simple, rapid, sensitive, and accurate method for detecting Escherichia coli O157:H7 in complex matrices is critical for ensuring food safety. In this study, a fluorescent biosensor employing aptamer (Apt) -functionalized magnetic beads and cascade strand displacement amplification (SDA) was devised for the detection of E. coli O157:H7 in milk samples. E. coli O157:H7 is captured by the aptamer, causing the complementary DNA (cDNA) to not bind to the aptamer and to be released into the supernatant. Following magnetic separation, the cDNA present in the supernatant initiates the opening of the hairpin (HP) structures. This enables primers to attach to the opened HP, triggering the initial SDA process, which generates a substantial quantity of double-stranded DNA (dsDNA) and recycles cDNA to open more HP structures. The dsDNA activates a second SDA, producing single-stranded DNA (ssDNA) for template binding and instigating a third SDA process. Triple SDA leads to the production of numerous G-quadruplex sequences and the formation of a G-quadruplex structure in the presence of K+. The inclusion of ThT into the G-quadruplex significantly enhances fluorescence. Under optimal conditions, this approach can detect E. coli O157:H7 at levels as low as 101 CFU/mL in pure cultures within 2.5 h, with a broad linear detection range of 101–106 CFU/mL. This method exhibits remarkable specificity towards the target bacteria over non-target bacteria. Furthermore, the technique has been effectively utilized for the detection of E. coli O157:H7 in milk samples. Notably, the method involves only two main steps, identification and amplification, significantly reducing contamination risks and minimizing operational steps.

Sensitive fluorescence detection of glyphosate and glufosinate ammonium pesticides by purine-hydrazone-Cu2+ complex

Organophosphorus pesticides play an important role as broad-spectrum inactivating herbicides in agriculture. Developing a method for rapid and efficient organophosphorus pesticides detection is still urgent due to the increasing concern on food safety. An organo-probe (ZDA), synthesized by purine hydrazone derivative and 2,2′-dipyridylamine derivative, was applied in sensitive recognition of Cu2+ with detection limit of 300 nM. Mechanism study via density functional theory (DFT) and job’s plot experiment revealed that ZDA and Cu2+ ions form a 1:2 complex quenching the fluorescence emission. Moreover, this fluorescent complex ZDA-Cu2+ was applicable for detecting glyphosate and glufosinate ammonium following fluorescence enhancement mechanism, with detection limits of 11.26 nM and 11.5 nM, respectively. Meanwhile, ZDA-Cu2+ was effective and sensitive when it is used for pesticide detection, reaching the maximum value and stabilizing in 1 min. Finally, the ZDA-Cu2+ probe could also be tolerated in cell assay environment, implying potential bio-application.

Peroxidase-like Activity of Aptamer-Gold Nanoparticles for Selective and Sensitive Fluorescence Detection of Low-Density Lipoproteins

Peroxidase-like Activity of Aptamer-Gold Nanoparticles for Selective and Sensitive Fluorescence Detection of Low-Density Lipoproteins

A "Pincer" Type of Acridine-Triazole Fluorescent Dye for Iodine Detection by Both 'Naked-Eye' Colorimetric and Fluorometric Modes.

Iodine, primarily in the form of iodide (I-), is the bioavailable form for the thyroid in the human body. Both deficiency and excess intake of iodide can lead to serious health issues, such as thyroid disease. Selecting iodide ions among anions has been a significant challenge for decades due to interference from other anions. In this study, we designed and synthesized a new pincer-type acridine-triazole fluorescent probe (probe 1) with an acridine ring as a spacer and a triazole as a linking arm attached to two naphthol groups. This probe can selectively recognize iodide ions in a mixed solvent of THF/H2O (v/v, 9/1), changing its color from colorless to light yellow, making it suitable for highly sensitive and selective colorimetric and fluorescent detection in water systems. We also synthesized another molecular tweezer-type acridine-triazole fluorescent probe (probe 2) that exhibits uniform detection characteristics for iodide ions in the acetonitrile system. Interestingly, compared to probe 2, probe 1 can be detected by the naked eye due to its circulation effect, providing a simple method for iodine detection. The detection limit of probe 1 is determined to be 10-8 mol·L-1 by spectrometric titration and isothermal titration calorimetry measurements. The binding stoichiometry between probe 1 and iodide ions is calculated to be 1:1 by these methods, and the binding constant is 2 × 105 mol·L-1.

APTES and CTAB Synergistic Induce a Heterozygous CsPbBr3/Cs4PbBr6 Perovskite Composite and its Application on the Sensitive Fluorescent Detection of Iodide ions.

Recently, all-inorganic halide perovskite quantum dots (IPQD) as a new fluorescent material with excellent fluorescence properties have attracted wide attention. However, their instability in polar solvents is the main factor hindering their application in analysis. Herein, a heterozygous perovskite (CsPbBr3/Cs4PbBr6) was simultaneously prepared and stabilized by a silylanization strategy using (3-aminopropyl)-triethoxysilane (APTES) and cetyltrimethyl ammonium bromide (CTAB) assisted precipitation encapsulation method. The synthesized CsPbBr3/Cs4PbBr6 emitted an independent fluorescence at 520nm. The obtained CsPbBr3/Cs4PbBr6 exhibited good stability in ethanol/water mixtures. It was used as a fluorescent probe for sensitively detecting iodide ions (I-) by fluorescence quenching mechanism in the concentration range of 1 ~ 70.0 µM with the detection limit (LOD) of 0.83 µM (relative standard deviation (RSD) = 1.33%, n = 20). The simplicity and high selectivity of the proposed fluorescent analysis method were the prominent features. This work could be extended to the other target ion detection by a perovskite fluorescent quenching.

Sodium dodecyl sulfate-modified ZIF-8 for sensitive detection of tetracycline in foods under synergistic adsorption of sodium dodecyl sulfate

The abuse for tetracycline (TC) in animal husbandry causes the residue of TC in animal foods, and even in vegetables arised from the pollution of soil. The sensitive determination of TC is greatly significant for the safety monitoring of foods. Herein, sodium dodecyl sulfate (SDS) was self-assembled on zeolite imidazolate framework-8 (ZIF-8) via hydrophobic interaction. The sensitive fluorescent detection of TC was obtained based on ZIF-8@SDS as-synthesized. After adding TC to ZIF-8@SDS, the internal ZIF-8 sensitized the emission band of TC centered at 521 nm, and the external SDS adsorbed TC via hydrophobic and electrostatic interactions. On this basis, TC could be quantified by ZIF-8@SDS selectively in a concentration range from 0.01 to 60 μM within 1 min. Importantly, the synergistic adsorption effect of SDS promoted the sensitivity of ZIF-8@SDS, and the limit of detection as low as 9 nM was calculated toward TC. The concentrations of TC in fish and tomato samples were determined by ZIF-8@SDS. The relative standard deviations ranged from 1.1 % to 6.7 %, and the spiked recoveries were in the range of 85.2 %–116.2 %, proving the application potential of ZIF-8@SDS in food safety monitoring.

Rapid and highly sensitive fluorescent detection of protamine and trypsin activity with Eosin B

A highly sensitive detection system for protamine and trypsin activity was developed using a commercially available anionic fluorescent dye, Eosin B (EB), as the probe. EB exhibited a highly sensitive colorimetric and fluorescent response for visual detection of protamine with a good selectivity over other interfering substances in the 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer (10 mM, pH 7.4). A linear relationship between the fluorescence intensity and protamine concentration was obtained ranging from 0 to10 μg/mL with a detection limit of 29.25 ng/mL. The presence of trypsin hydrolyzed protamine, leading to the release of EB from EB-protamine complex. The fluorescence recovery of EB can monitor the trypsin activity with satisfactory selectivity and sensitivity. The introduction of a trypsin inhibitor affected the recovery of the fluorescence. Thus, this detection system supplied a method for trypsin inhibitor screening.

Molecular Engineering of Bright NIR-I/NIR-II Nanofluorophores for High-Resolution Bioimaging and Tumor Detection in Vivo.

A comprehensive approach for the construction of NIR-I/NIR-II nanofluorophores with exceptional brightness and excellent chemo- and photostability has been developed. This study first confirmed that the amphiphilic molecules with stronger hydrophobic moieties and weaker hydrophilic moieties are superior candidates for constructing brighter nanofluorophores, which are attributed to its higher efficiency in suppressing the intramolecular charge transfer/aggregation-caused fluorescence quenching of donor-acceptor-donor type fluorophores. The prepared nanofluorophore demonstrates a fluorescence quantum yield exceeding 4.5% in aqueous solution and exhibits a strong NIR-II tail emission up to 1300 nm. The superior performance of the nanofluorophore enabled the achievement of high-resolution whole-body vessel imaging and brain vessel imaging, as well as high-contrast fluorescence imaging of the lymphatic system in vivo. Furthermore, their potential for highly sensitive fluorescence detection of tiny tumors in vivo has been successfully confirmed, thus supporting their future applications in precise fluorescence imaging-guided surgery in the early stages of cancer.

Chemical surface modification of carbon dots with Germanium: A highly sensitive and selective ratiometric fluorescence probe for Mg2+ detection using DFT and TD-DFT

In this study, we chemically modified carbon dots (Cdots) using germanium, enhancing their sensitivity and selectivity as a ratiometric fluorescence probe for precise detection of Mg2+ ions. Excitation of the modified Cdots resulted in a distinct emission peak at 527 nm, enabling accurate measurement of Mg2+ concentrations across a linear range. The surface modification with germanium led to the creation of novel emitting centers on the Cdots' surface. Theoretical calculations using density functional theory (DFT) revealed the effective suppression of these emitting centers through a photo-induced electron transfer (PET) process, utilizing the nitrogen lone pair electrons on the Cdots' surface. Furthermore, adjacent Cdots' surface pyrazino[2,3-f][1,10]-phenanthroline (PPT) nitrogen atoms formed chemical bonds with Mg2+ ions, resulting in the formation of aggregated Cdots. Consequently, the intricate complexation terminated the PET process, resulting in a novel emission peak at longer wavelengths. This study presents a highly sensitive and selective ratiometric fluorescent detection system with exceptional low concentration detection limit for precise Mg2+ ion detection.

Sensitive fluorescence detection based on dimeric G-quadruplex combined with enzyme-assisted solid-phase microextraction of streptomycin in honey

Streptomycin (STR), an aminoglycoside antibiotic with the potential to persist in honey and other food products, may induce allergy, toxicity and antibiotic resistance in humans. In this study, we developed a solid-phase microextraction (SPME) biosensor based on a quartz rod that was modified with double-stranded DNA structures consisting of partially complementary G-rich base DNA strand and STR aptamer. The STR isolated by SPME initially bound to the aptamer. Then the remaining double-stranded DNA structures were cleaved by the Nt.BstNBI enzyme, resulting in release of G-quadruplex dimers. The latter formed a complex with thioflain T fluorescent dye, resulting in an amplified fluorescence response. The method exhibited high sensitivity (a limit of detection of 10.84 pM), wide linear range (0.05 nM ∼ 500 nM (with determination coefficient > 0.99)), and simple operation, making it suitable and convenient for STR detection. Successful STR determination in genuine honey samples was demonstrated.

Non‐invasive and Sensitive Fluorescence Detection of Phenylpyruvic Acid via a Guanidinomethyl‐modified Calixarene

AbstractDetection of phenylpyruvic acid (PPA) is important for the diagnosis of phenylketonuria (PKU). In this study, we designed a guanidinomethyl‐modified calix[5]arene that can strongly and selectively bind with PPA. Via indicator displacement assay, we set up a calibration line for accurately determining PPA concentration down to the μM range in artificial urine based on the linear relationship between the fluorescence intensity and PPA concentration. This work provides a low‐cost, easy‐to‐operate, rapid, and sensitive method for PPA detection, and may offer an alternative for PKU diagnosis in clinical study.

Ionic Polyimine-Based Composite Membrane with Inductive and Complexation Synergistic Effects for Sensitive and On-Site Fluorescent Detection of Volatile Iodine.

Along with the development of nuclear power, concerns about radioactive emissions and the potential for nuclear leakage have been widely raised, particularly of harmful iodine isotopes. However, as a significant component of nuclear air waste, the enrichment and detection of air-dispersed gaseous iodine remain a challenge. In this work, it is focused on developing an attraction-immobilization-detection strategy-based fluorescence method for the on-site detection of volatile iodine, by employing a photoluminescent ionic polyimine network-polyvinylpyrrolidone (IPIN-PVP) composite membrane. This strategy synergizes ion-induced dipole interactions from IPIN and complexation effects from PVP, allowing effective iodine enrichment and immobilization. As a result, the optimized IPIN-PVP membrane exhibits rapid response times of 5 s and a low detection limit of 4.087 × 10-8m for gaseous iodine. It also introduces a portable handheld detection device that utilizes the composite membrane, offering a practical solution for real-time on-site detection of volatile iodine. This innovation enhances nuclear safety measures and disaster management by providing rapid and reliable iodine detection capabilities.

Selective fluorescence detection of acetylsalicylic acid, succinic acid and ascorbic acid based on a responsive lanthanide metal fluorescent coordination polymer.

A fluorescent sensor for highly selective and ultrasensitive detection of acetylsalicylic acid (ASA), succinic acid (SA), and ascorbic acid (AA) was reported. The water-soluble fluorescent ligand salicylic acid (Sal) was generated through catalyzing ASA by the hydrolase activity of zeolitic-imidazolate framework-8 (ZIF-8) or natural esterase (Est). The Sal can coordinate with 2-methylimidazole (2-MIm) and Ln(III) to form a fluorescent lanthanide coordination polymer (LCP), which has a fluorescence emission peak with the maximum wavelength at 412 nm (the excitation wavelength at 300 nm). Therefore, the detection of ASA can be achieved through the fluorescence intensity changes of LCPs in the system, which has comparable sensitivity and good selectivity (linear range of 0.031-1.00 mM and LODs of 11.72 and 3.22 μM) as compared to a direct reaction between Est/ZIF-8 and ASA for detecting ASA (linear range of 0.05-1.20 mM and limits of detection (LODs) of 4.43 and 4.58 μM). Furthermore, upon the addition of SA and AA, the fluorescence intensity of the reaction system can be enhanced and weakened through changing the energy resonance transfer pathways and affecting the enzymatic reaction process, respectively, realizing their sensitive and selective fluorescence detection. The established fluorescent sensors can work well in a wide linear range of SA concentrations from 0 to 2.50 mM (Est-based reaction system) and 0 to 1.50 mM (ZIF-8-based reaction system) with the LODs of 0.032 and 0.028 mM, respectively. The linear ranges of AA concentrations are from 0.0078 to 0.25 mM (Est-based reaction system) and 0.0078 to 0.13 mM (ZIF-8-based reaction system) with the LODs of 2.54 and 3.80 μM, respectively. The established sensors were successfully used in the detection of SA in rabbit plasma, with a recovery of 84.0%-98.7%. Additionally, the contents of ASA in Aspirin Enteric-Coated tablets and AA in vitamin C tablets were also determined by the developed methods.

Accurate and sensitive dual-response fluorescence detection of microRNAs based on an upconversion nanoamplicon with red emission.

Oral squamous cell carcinoma (OSCC) is the most common type of oral cancer. In recent years, researchers have found a close relationship between microRNAs (miRNAs) and OSCC. In addition, miRNAs are highly stable in tissues and circulation, and are also considered potential biomarkers for cancer detection and prognosis. Among a variety of tools for miRNAs with low abundance, single red-emitting UCNP-based biosensors have attracted special interest due to their unique properties, including deep organizational penetration, weak radiation damage, and low autofluorescence. Additionally, the measurement of low-abundance analytes via enzyme-free signal amplification is also an effective means. Herein, by taking advantage of red-emitting UCNPs and an enzyme-toehold-mediated strand displacement cascade, a dual-signal amplification biosensor was constructed. The recycled miRNA can be regarded as a catalyst for the assembly of multiple H1/H2 duplexes, which promoted the response signal of augmented analyte expression. Moreover, the proposed biosensors improved the measurement accuracy via a dual-signal response to obviously avert false-positive signals. The proposed method was applied to measure miRNA-222 (a model analyte) in serum samples, and the results were similar to those of polymerase chain reaction (PCR), with spiked recoveries ranging from 91.2% to 101.7%. The proposed assay has the merits of high sensitivity, strong recognition, and low background, indicating broad potential for the measurement of diverse analytes in biological samples.

Highly sensitive fluorescent explosives detection via SERS: based on fluorescence quenching of graphene oxide@Ag composite aerogels.

High fluorescence background poses a substantial challenge to surface-enhanced Raman scattering (SERS), thereby limiting its broader applicability across diverse domains. In this work, silver nanoparticle (Ag NP)-loaded graphene oxide aerogel nanomaterials (GO-Ag ANM) were prepared for sensitive SERS detection of fluorescent explosive 2,4,8,10-tetranitrobenzo-1,3a,6,6a-tetraazapentaenopyridine (BPTAP) by a fluorescence quenching strategy. By harnessing the fluorescence quenching properties of graphene and the localized surface plasmon resonance of silver nanoparticles, the synthesized aerogels exhibited effective fluorescence quenching and Raman enhancement capabilities when employed for BPTAP analysis with 532 nm laser excitation. Significantly, precise control over the loading quantity of silver nanoparticles (Ag NPs) resulted in the remarkable sensitivity of the surface-enhanced Raman scattering (SERS) effect. This method allowed for the detection of fluorescent explosive BPTAP at an extraordinarily low concentration of 1 × 10-7 M. Furthermore, the approach also demonstrated excellent detection capabilities for the dyes R6G, CV, and RhB. This study offers valuable insights for the sensitive detection of fluorescent molecules.

Green one-step pyrolytic synthesis of folic acid-derived carbon dots for sensitive turn-on fluorescence detection of cysteine.

The purpose of the present study is to develop an easy and effective one-step pyrolytic method for synthesizing carbon dots (CDs) derived from folic acid (FA), denoted herein as FACDs. This method is green, inexpensive, and simplifies the synthesis of fluorescent carbon nanomaterials with enhanced and stable fluorescence. Moreover, the as-prepared FACDs are effective in the sensitive and selective detection of cysteine (Cys) by such a "turn-on" mechanism of fluorescence. FACDs have been able to realize a low detection limit of 1.7 × 10-7 M and a wide linear range from 5.0 × 10-7 to 8.0 × 10-5 M, successfully restoring quenched fluorescence in the presence of Cys. Obtained results confirm FACDs as a trustful high-performance sensor for various biological and environmental applications and pave the way for facile and efficient fluorescence-based detection platforms.