Internal Filter Effect Research Articles

The fabrication of fluorescent sensor for Fe3+ detection and configurable logic gate operation based on N-doped carbon dots

Herein, fluorescent N-doped carbon dots (N-CDs) were obtained using hydrothermal treatment of polyethyleneimine and melamine. The N-CDs exhibit nanoscale structure, good water solubility, photostability and excellent fluorescence property with a high fluorescence quantum yield of 26 %. The as-prepared N-CDs were selected for the detection of Fe3+ with a fluorescence “OFF-ON” strategy by the mechanism of internal filtration effect (IFE). A good linear relationship can be observed for the concentration of Fe3+ from 0 to 500 μM, and the calculated detection limit (LOD) for Fe3+ was 0.88 μM (3σ/slope). Meanwhile, the N-CDs based sensor can be utilized for tracing Fe3+ in real water samples. In addition, the quenched fluorescence can be recovered with the treatment of l-cysteine, and thus can be designed for quantitative determination of l-cysteine with a fluorescent “ON-OFF-ON” switch. Moreover, a set of resettable, multireadout logic gate operations including OR and AND have been realized for the N-CDs.

Dual-emission carbon dots for ratiometric fluorescence sensing of thiabendazole in fruits

Quantitative determination of pesticides in fruits and vegetables is essential for human healths. Herein, a new dual-emission carbon dots with high fluorescence stability at a pH range of 4–10 and a temperature range of 0–60 °C was synthesized. And a novel ratiometric fluorescence probe was proposed to detect thiabendazole (TBZ) residue with a wide linear range (0–1000 μM) and low detection limit (0.15 μM). The emission at 512 nm exhibited a special “turn-off” fluorescence sensing of TBZ due to internal filter effect, while that at 361 nm barely changed and worked as reference. Furthermore, the ratiometric fluorescence strategy was successfully applied for determining TBZ in fruits with good recoveries (96.73%–111.17 %, 93.29%–120.78 % and 96.28%–100.57 %, respectively). Notably, the constructed ratiometric fluorescence probe had comparable accuracy to HPLC in detecting unknown concentrations of TBZ in pear juice, demonstrating dual-emission carbon dots possess wide and promising applicability for fluorescence sensing pesticides in the future.

A fluorescent sensor based on Zn(II)-coodination polymers bearing mixed ligands for the sensitive detection of riboflavine, imidacloprid and nitenpyram

Two new 2D Zn(II) coordination polymers (BAO28 and BAO29), formulated as [Zn(DIN)(HPT)]DMF·2H2O (BAO28) and [Zn(DIN)(HPT)]·2H2O (BAO29) (H2HPT = 5‑hydroxy-isophthalic acid, DIN = 1,4-di(imidazol-1-yl)naphthalene and DMF = N,N-dimethylformamide), were successfully synthesized under solvothermal conditions. Fluorescence analysis showed that BAO28 proceeded with a DIN ligand-based emissive fluorescence. More importantly, the recoverable multi-responsive fluorescent sensor BAO28 was used for fluorescent detection of imidacloprid (IMI), nitenpyram (NTP), and riboflavine (VB2) in a neutral buffer solution with high sensitivity and a low detection limit. Moreover, the sensing of the pesticides by BAO28 was mainly due to the competitive absorption of excitation and emission light by the sensor with that of the pesticides. Furthermore, for the sensing of riboflavine, in addition to the internal filtration effect (IFE) and fluorescence resonance energy transfer (FRET) mechanisms, the sensing mechanism was simultaneously attributed to photoinduced electron transfer.

BCNO quantum dots-based ratiometric fluorescence platform integrated with portable device: Hypoxanthine sensing for on-site assessment of meat freshness with deep learning

Deep learning algorithms have been applied to digital image colorimetry (DIC) to improve color measurement and analysis, enabling the identification and quantification of analytes. In this work, we developed a smartphone-assisted platform for the detection of hypoxanthine (Hx) based on a ratiometric fluorescent probe (RF-probe) and deep learning algorithm for the first time with advantages of high sensitivity, in-field and simple operation, and accurate detection. Through an enzymatic cascade reaction, xanthine oxidase (XOD) degraded Hx to uric acid (UA) and H2O2, o-phenylenediamine (OPD) was converted to 2,3-diaminophenoxazine (DAP) by catalytic oxidation of H2O2 and OPD under horseradish peroxidase (HRP). The presence of DAP led to fluorescence quenching of BCNO quantum dots (BCNO QDs) at 440 nm and fluorescence enhancement of DAP at 570 nm due to the internal filtration effect (IFE). With the addition of Hx, the fluorescence color changed from blue to yellow. A good linear relationship was between I570/I440 and the Hx concentration in the range of 3-100 µM with a detection limit of 50 nM. Fluorescent color images of solution and test strips were acquired and extracted with a smartphone of our designed miniature device, which could be used to establish DIC for the detection of Hx with the linear relationship ranging from 0-100 μM and 0-40 μM, respectively. Then YOLOv5-assisted deep learning was applied to recognize and deal with the images, which offered improved accuracy, faster inference speed, flexibility, and efficient training. Therefore, our simple DIC platform was established for the in-field detection of Hx in real meat samples which was significant for the analysis of meat freshness and provided broad application potential for the analysis of other targets in food safety.

4-Mercaptobenzoic acid coated self-assembled aggregative luminescent copper nanoclusters for the detection of ethyl vanillin

Ethyl vanillin (EVA) is a food additive with strict requirements, and the addition of more than the standard will affect the human body, so the design of a fast and sensitive detection method for EVA has aroused people's interest. Here, we developed a fluorescence assay method for the sensitive detection of EVA by 4-mercaptobenzoic acid (4-MBA) coated self-assembled copper nanoclusters (4-MBA-CuNCs). Under alkaline conditions, 4-MBA-CuNCs self-assembled aggregation induces strong blue fluorescence, and its quantum yield is 5.51 %. Under very simple conditions, the fluorescence intensity of 4-MBA-CuNCs at 421 nm was reduced by EVA through static quenching and internal filtration effect. The detection method showed a good linear relationship between 0.1 and 5.1 μM, and its detection limit was 30 nM. Moreover, the preparation of 4-MBA-CuNCs could provide a simple and quick method for the detection of EVA in real samples.

Dual-mode fluorescence and colorimetric sensing of sulfide anion in natural water based on near-infrared Ag2S quantum dots and MnO2 nanosheets complex

Near infrared (NIR) emission Ag2S quantum dots (QDs) are of great value for biochemical sensing with strong anti-interference and low toxicity. Herein, NIR fluorescence Ag2S QDs were synthesized successfully. Combined with the excellent oxidase-like characteristics of manganese dioxide (MnO2) nanosheets, a fluorescence and colorimetric dual-mode sensor for sulfide anion was developed. MnO2 nanosheets could effectively catalyze the oxidation of TMB to produce blue TMB oxide (ox TMB), at the same time, the fluorescence of Ag2S QDs could be effectively quenched by fluorescence internal filtration effect (IFE) and dynamic quenching effect. The enzyme-like activity was weakened and the NIR fluorescence of Ag2S QDs was restored when sulfide anion (S2−) was added, due to the reduction of MnO2 to Mn2+.The linear ranges for fluorescence and colorimetric analysis of S2− were 2–250 μM and 0.3–50 μM, with detection limits of 0.6 and 0.215 μM, correspondingly. The dual-mode sensor had a wider detection range, higher sensitivity and shorter reaction time, which could be used for highly selective detection of S2− in different concentration ranges. In addition, it had been successfully applied to the determination of sulfide in water samples with satisfactory accuracy and sensitivity.

Single-atom Cu-attached MOFs as peroxide-like enzymes to construct dual-mode immunosensors for detection of breast cancer typing in serum

Molecular subtype of breast cancer has defined the treatment direction of breast cancer and guided the selection of drugs. Invasive tests such as tissue biopsy have the potential to promote the metastasis of cancer cells. Therefore, the continuous development of high-performance and low-cost in vitro diagnostic tools is crucial for the diagnosis and treatment of cancer prognosis. Liquid biopsy techniques provide noninvasive, real-time, dynamic, multicomponent, quantitative, and long-term observations at the cellular, genetic, and molecular levels in vivo. A Cu-Zr metal-organic framework(MOF) nanomases with monatomic Cu attachment has been synthesized by covalently attaching single atom Cu to the defect site of zirconia clusters in the UiO-66. The catalytic performance of Cu/UiO-66 as a peroxide-like enzyme was verified by enzyme kinetics calculation. Using o-phenylenediamine as substrate, a colorimetric fluorescence dual-mode immunosensor was constructed by introducing blue fluorescent carbon quantum dots (CDs) based on ultraviolet chromogenic reaction and fluorescence internal filtration effect. By magnetic adsorption separation, the background signal of the sensor is reduced and the sensitivity of the sensor is further improved. In 0.001–1 ng/mL detection range, detection of HER2/ER/PR/Ki-67, the result has obvious linear relationship. Among them, the colorimetric detection limit were 0.367/0.379/0.392/0.388 pg/mL; the ratio fluorescence detection limit can reach 0.3, 0.289, 0.257, 0.33 pg/mL, with high sensitivity. The proteins HER2, ER, PR and Ki-67 in serum related to human breast cancer typing were detected with high sensitivity. Finally, the actual serum samples were tested using sensors. According to the confirmed detection criteria, the classification of serum breast cancer was preliminarily explored with an accuracy of 87.5 %. The sensor has high catalytic performance and excellent real-time detection performance of biomarkers, and have practical application potential in human serum level detection. It provides a new method for the classification of breast cancer in serum.

Studying Fluorescence Sensing of Acetone and Tryptophan and Antibacterial Properties Based on Zinc-Based Triple Interpenetrating Metal-Organic Skeletons.

Two triple interpenetrating Zn(II)-based MOFs were studied in this paper. Named [Zn6(1,4-bpeb)4(IPA)6(H2O)]n (MOF-1) and {[Zn3(1,4-bpeb)1.5(DDBA)3]n·2DMF} (MOF-2), {1,4-bpeb = 1,4-bis [2-(4-pyridy1) ethenyl]benze, IPA = Isophthalic acid, DDBA = 3,3'-Azodibenzoic acid}, they were synthesized by the hydrothermal method and were characterized and stability tested. The results showed that MOF-1 had good acid-base stability and solvent stability. Furthermore, MOF-1 had excellent green fluorescence and with different phenomena in different solvents, which was almost completely quenched in acetone. Based on this phenomenon, an acetone sensing test was carried out, where the detection limit of acetone was calculated to be 0.00365% (volume ratio). Excitingly, the MOF-1 could also be used as a proportional fluorescent probe to specifically detect tryptophan, with a calculated detection limit of 34.84 μM. Furthermore, the mechanism was explained through energy transfer and competitive absorption (fluorescence resonance energy transfer (FRET)) and internal filtration effect (IFE). For antibacterial purposes, the minimum inhibitory concentrations of MOF-1 against Escherichia coli and Staphylococcus aureus were 19.52 µg/mL and 39.06 µg/mL, respectively, and the minimum inhibitory concentrations of MOF-2 against Escherichia coli and Staphylococcus aureus were 68.36 µg/mL and 136.72 µg/mL, respectively.

Ratiometric upconversion luminescence sensing platform for visual monitoring of antiarrhythmic drug level in serum

Arrhythmia seriously threatens life and health, it requires long-term use of antiarrhythmic drugs such as mexiletine and needs to monitor the dosage of drugs in the body to ensure efficacy and avoid serious side effects. Here, we designed a sensing platform for real-time visual monitoring of drug efficacy using a ratiometric upconversion probe, which overcomes the fluorescence background interference in the serum, and improves the resolution and accuracy of visual detection. By combining lanthanide-doped upconversion nanoparticles (UCNPs) with readily available organic dyes, an efficient upconversion nanoprobe was constructed under the reaction mechanism of internal filtration effect (IFE) to realize the quantitative detection of mexiletine in serum. Due to the addition of mexiletine, the characteristic emission peak of the probe at 540 nm changes, while the fluorescence intensity at 655 nm is unchanged. Therefore, the visual detection of mexiletine in serum is realized according to the fluorescence intensity changes of I540/I655. In addition, the designed sensing platform is combined with a smartphone to realize real-time visualization and quantitative monitoring of mexiletine, and the detection limits in fluorescence and colorimetric modes are as low as 55.6 nM and 469.75 nM respectively, consequently resulting in sensitive monitoring the effective dosage of drugs in the serum. The proposed detection platform provides a new sensing strategy for the visual determination of antiarrhythmic drugs and an instant device to warn the treatment process of the disease immediately.

Highly sensitive detection for xanthine by combining single-band red up-conversion nanoparticles and cycle signal amplification strategy based on internal filtration effect

Up-conversion nanoparticles (UCNPs), especially single-band bright red UCNPs, have better penetration of biological tissues, absorb less lost energy, and have higher sensitivity and accuracy in the determination of actual biological samples in the field of biosensing. Here, a novel colorimetric and fluorescent dual-channel method based upon an internal filtration effect (IFE) quenching mechanism was proposed for the quantitative analysis of xanthine (XA) by using red UCNPs as fluorescence indicator and 3,3′,5,5′ -tetramethylbenzidine (TMB) as chromogenic substrate. The sensitivity of the detection system was also enhanced by a cycle signal amplification strategy based on the Fenton reaction. Under the best conditions, the detection limits of XA by fluorescent and colorimetric methods were 0.58 μM and 1.19 μM, respectively. The developed method was applied to the detection of XA in actual serum samples, and the recoveries of the spiked samples by fluorescent and colorimetric methods were in the range of 96.3–104.3 % and 94.3–105.4 %, respectively. In addition, the commercial ELISA method was used to verify the application of the proposed method and the test results of XA were close to those obtained by fluorescent and colorimetric methods, indicating that the accuracy of the developed nanosensing system was acceptable.

An accurate and sensitive sensor based on the internal filtration effect for the detection of alkaline phosphatase and ascorbic acid by the Fenton reaction and dual readout signal

Ascorbic acid (AA) and alkaline phosphatase (ALP) in human serum are indispensable substances in the process of biological metabolism, and their abnormal contents are strongly associated with a range of diseases. Therefore, it is meaningful to develop a simple, accurate and sensitive assay for the detection of AA and ALP. Up-conversion nanoparticles (UCNPs) have some unique characteristics, especially, the potential for background-free excitation by the near-infrared region (NIR) significantly improves the limits of detection (LODs). Moreover, sensors based on the inner filter effect (IFE) do not require covalent linkage between receptors and fluorophores or surface modification, thus the probe fabrication is simple and flexible UCNP-based. Therefore, a simple, selective, sensitive, and flexible sensing system for the detection of AA and ALP is proposed by combining the IFE and the cyclic signal amplification strategy. Under ideal circumstances, the LODs of ALP through the colorimetric and fluorescence method were 0.192 U/L and 0.013 U/L. The established sensing platform was applied to assessing ALP activity in human serum, and the detection results are close to those of commercially available kits, indicating its immense potential as an effective and convenient tool for monitoring ALP activity in clinical settings.

Ultrasensitive fluorescent carbon dot sensor for quantification of soluble and insoluble Cr(VI) in particulate matter

This study investigates advanced functional materials to address the need for practical and affordable analytical techniques for monitoring large amounts of insoluble Cr(VI). N,S-doped fluorescent carbon dots (f-CDs) were fabricated through microwave synthesis, with an average diameter of 10 nm. These f-CDs were explored as potential sensors for detecting Cr(VI) in ambient particulate matter (PM). Laboratory experiments yielded positive results, showing average recoveries of 106.0%, 102.3%, 96.4%, and 101.7% for PbCrO4, BaCrO4, CaCrO4, and (NH4)2CrO4, respectively. Applying the fluorescence method to field PM samples, a method detection limit (MDL) of 0.32 ng/m3 for total Cr(VI) quantification was achieved. The fluorescence decay of carbon dots remained stable over time, suggesting that Cr(VI) quenching primarily occurred due to the internal filter effect through a static quenching mechanism. These f-CDs exhibited advantageous properties, including affordability, solubility, luminescence, and sensitivity, positioning them as a promising alternative for Cr(VI) detection in ambient air particulates. This study contributes to further developing carbon-based functional materials for detecting metallic air pollutants.

Machine learning integrated high quantum yield blue light carbon dots for real-time and on-site detection of Cr(VI) in groundwater and drinking water

The safety of groundwater and drinking water is directly related to the well-being of human beings and ecosystems. On-site monitoring and timely response to heavy metals in these water sources are crucial for water supply security. Fluorescent probes combined with machine learning technology have been applied to on-site detection of heavy metals. However, they were primarily focused on industrial-level detection and lacked the sensitivity required for detecting Cr(VI) in groundwater and drinking water. In this study, we developed an machine learning-integrated approach using high-quantum-yield (QY) N-doped blue-light carbon dots (N-BCDs) for instant detection of Cr(VI) in groundwater and drinking water. N-BCDs were synthesized within 3 min using a household microwave oven with citric acid and 1,2-diaminobenzene, resulting in a QY of approximately 90 %. The fluorescence of N-BCDs was quenched via the internal filter effect (IFE), enabling the detection of Cr(VI) within 1 min, with a detection limit of 0.1574 μg L−1 for Cr(VI) concentrations ranging from 0 to 60 μg L−1. We employed machine learning methods to determine Cr(VI) concentrations from simple shots, based on the red-green-blue (RGB) feature and Kmeans feature extraction. These features were input into four models (Ridge, XGB, SVR, and Linear), achieving a fitness of 95.2 %. Furthermore, the accuracies for Cr(VI) concentration identification in actual groundwater and drinking water were as high as 95.71 % and 96.81 %, respectively. Our work successfully extended the detection range of Cr(VI) to the μg level, significantly improving the practical applicability of the method and providing a new approach for on-site detection of Cr(VI) in groundwater and drinking water.

Synthesis of Fluorescent Carbon Quantum Dots based on Boletus speciosus and Analysis of Metronidazole

Background: Metronidazole is widely used due to its clinical excellence in treating systemic or local infections caused by anaerobic bacteria. However, it is easily soluble in water, not easy to biodegrade and adsorb and stays for a long time in environments, causing great harm to human health and food safety. Therefore, it is important to choose highly selective and sensitive methods for metronidazole content determination in environments. In this paper, the edible fungus Boletus speciosus was used as the carbon precursor to successfully prepare carbon dots by one-step hydrothermal method, and were used to analyze metronidazole. Methods: Characterization of the prepared carbon dots from B. speciosus (Bs-CDs) were studied by Transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and X-Ray Diffraction. Results: The linear equation was y=0.06231+0.01099x (R2=0.9970) with a metronidazole concentration of 2.5~50 μM, and the detection limit was 71 nM. The fluorescence quenching mechanism of Bs-CDs detecting metronidazole belonged to the internal filtration effect. Bs-CDs were applied to detect metronidazole in actual water samples, presenting good sensitivity and a high recovery rate (97.0~106.0%). Conclusion: This method provides a new idea for the application of carbon dots in metronidazole content detection.

A nanozyme-linked immunosorbent assay based on Au@CeO2@Pt nanozymes for colorimetric and fluorescent detection of SARS-CoV-2 nucleocapsid protein

Developing powerful alternatives to natural enzymes has been a target pursued by researchers, and nanozymes are considered to be the best candidate due to their unique advantages of high stability, high activity, and easy modification. In this study, the multishell complexes of Au@CeO2@Pt nanozymes were successfully synthesized which exhibited an excellent intrinsic peroxidase-like ability to oxidize 3,3′,5,5′-tetramethylbenzidine (TMB), and resulting in a visible colorimetric signal. Interestingly, due to the internal filtration effect, the blue-emitting oxidized TMB (oxTMB) can also quench the red-emitting light from bimetallic AuAg nanoclusters. Based on the above properties, a kind of robust immunoassay for target protein detection was established. The dual-mode immunoassay is more accurate for SARS-CoV-2 detection on account of the reciprocal corroboration of the signals. More importantly, the immunoassay had high sensitivity with a low limit of detection and excellent recovery rates in simulated urine/saliva samples. Therefore, it is highly anticipated the immunoassay based on the newly developed nanozyme became an accurate instrument for diagnosing SARS-CoV-2 in the biomedical field.

A novel sustainable biomass-based fluorescent probe for sensitive detection of salicylic acid in rice

Herein, a ratiometric fluorescent probe was developed for sensitive detection of salicylic acid (SA) in rice using silk-derived carbon quantum dots @ Curcumin @ iron-based metal organic framework (SCQDs@Cur@Fe-MOFs). Fe-MOFs with porous structure not only provided holes for SCQDs to evade self-aggregation of SCQDs, but Fe2+ ions from MOFs was ingeniously employed to capture active sites of Cur, solving the problem of lacking sufficient specificity of Cur to SA while converting weak response signal to amplified “turn on” mode. Upon exposed to SA, the probe interacted with SA to form Cur-Fe2+-SA ternary complex, which inhibited the internal filtration effect between Cur and SCQDs, and triggered a cascade of response signaling. With this strategy, the proposed probe achieved sensitive determination of salicylic acid in rice with detection limit as low as 0.14 μmol/L. This study provides unique insight into constructing economical and eco-friendly fluorescent sensor for SA detection with superior performance.

Fe-MOF-based fluorescent sensor with on/off capabilities for the highly sensitive detection of tert-butylhydroquinone in edible oils

In this work, a “turn off-on” fluorescent sensor was developed for highly sensitive determination of tert-butylhydroquinone (TBHQ) based on an Fe(III)-based metal-organic framework (Fe-MOF). An Fe-MOF with an octahedral structure was synthesized via a simple hydrothermal method using ferric chloride hexahydrate and 2-aminoterephthalic acid (NH2-BDC) as raw materials. The fluorescence of Fe-MOF is extremely weak owing to ligand-to-metal charge transfer (LMCT) and internal filtration effect (IFE). When the system contained TBHQ, the binding of TBHQ to Fe(III) inhibited the LMCT of the fluorescent ligand NH2-BDC to Fe(III), releasing the fluorescence of NH2-BDC and thus restoring the fluorescence. With this as the basis, a rapid, sensitive, and selective fluorescence sensor is developed for the detection of TBHQ. Under the optimal conditions, TBHQ showed good linearity with fluorescence intensity in the range of 0–1.5 × 102 μmol L−1 and a detection limit of 0.0030 μmol L−1 (S/N = 3). The selectivity, reproducibility, and stability of the developed Fe-MOF-based sensors are comprehensively studied. Finally, the practicality of the method is verified by examining the detection of TBHQ in soybean oil; the results are consistent with those obtained using conventional high-performance liquid chromatography.

Dual-Functional Eu-Metal-Organic Framework with Ratiometric Fluorescent Broad-Spectrum Sensing of Benzophenone-like Ultraviolet Filters and High Proton Conduction.

The construction of attractive dual-functional lanthanide-based metal-organic frameworks (Ln-MOFs) with ratiometric fluorescent detection and proton conductivity is significant and challenging. Herein, a three-dimensional (3D) Eu-MOF, namely, [Eu4(HL)2(SBA)4(H2O)6]·9H2O, has been hydrothermally synthesized with a dual-ligand strategy, using (4-carboxypiperidyl)-N-methylenephosphonic acid (H3L = H2O3PCH2-NC5H9-COOH) and 4-sulfobenzoic acid monopotassium salt (KHSBA = KO3SC6H4COOH) as organic linkers. Eu-MOF showed ratiometric fluorescent broad-spectrum sensing of benzophenone-like ultraviolet filters (BP-like UVFs) with satisfactory sensitivity, selectivity, and low limits of detection in water/ethanol (1:1, v/v) solutions and real urine systems. A portable test paper was prepared for the convenience of actual detection. The potential sensing mechanisms were thoroughly analyzed by diversified experiments. The synergistic effect of the forbidden energy transfer from the ligand to Eu3+, the internal filtration effect (IFE), the formation of a complex, and weak interactions between the KHSBA ligand and BP-like UVFs is responsible for the ratiometric sensing effect. Meanwhile, Eu-MOF displayed relatively high proton conductivity of 2.60 × 10-4 S cm-1 at 368 K and 95% relative humidity (RH), making it a potential material for proton conduction. This work provides valuable guidance for the facile and effective design and construction of multifunctional Ln-MOFs with promising performance.

Detection of Doxycycline Using Carbon Quantum dots as Probe Based on Internal Filtering Effect.

The establishment of a convenient and effective detection method for doxycycline (DC) holds significant importance in drug monitoring and drug residue assessment. In this work, carbon quantum dots (CQDs) with excellent and stable luminescence performance (the quantum yield of CQDs was 21.8%) were synthesized by the melting method and employed as probes to monitor the fluorescence intensity variations before and after the introduction of DC. A fluorescence analytical method based on the internal filtration effect (IFE) was developed for DC determination. The mechanism of DC quenching CQDs was verified using fluorescence lifetime tests, absorption spectroscopy, and evaluation of internal filtration parameters. After optimizing experimental conditions, it was found that the DC concentration (CDC) exhibited a good linear relationship with the fluorescence quenching efficiency ((F0-F)/F0) of CQDs in the range of 5-30 µM. The fitted linear equation was Y = 0.01249*CDC+0.03625, R2 = 0.9987, and the detection limit was 2.343 µM (n = 8). This developed method has been successfully applied to accurately determine DC concentrations in both doxycycline hydrochloride tablets and human serum samples. It stands out for its simplicity, rapidity, and acceptable detection performance. Due to its advantages, this method holds great promise for application in the biomedical field for monitoring DC drug concentrations and ensuring quality control.

An upconversion fluorescent and colorimetric dual-mode optical probe for triazophos pesticides

A dual-mode optical probe for organophosphorus pesticides triazophos (TRP) was developed on the basis of internal filter effect (IFE) between upconversion nanoparticles NaYF4: Yb/Er @NaYF4@SiO2 (UCNPs) and gold nanoparticles (AuNPs) in the presence of protamine (PRO) and Trypsin (TRY). In this essay, AuNPs can quench significantly the fluorescence intensity of UCNPs at 550 nm with 980 nm excitation. PRO is a cationic protein that binds AuNPs effectively and aggregates AuNPs due to electrostatic attraction. The aggregation of AuNPs made the solution blue and the fluorescence intensity of UCNPs at 550 nm was recovered correspondingly. Furthermore, TRY could hydrolyze PRO, and PRO will reduce AuNPs clustering due to the addition of TRY, inducing the solution to purple and quench the fluorescence of UCNPs again. After adding the TRP, the activity of TRY was inhibited, thereby preventing PRO hydrolysis and causing AuNPs to reaggregate. Reassembled AuNPs restored the fluorescence of UCNPs again. The inhibition efficiency of fluorescence and colorimetric has a good linear relationship with the logarithmic TRP concentration in the range of 0.03∼300 ng/mL, and the detection limits are 0.0052 and 0.0026 ng/mL, respectively. In addition, the recovery of TRP in real food samples with satisfactory results ranged from 96.02 to 104.30% and 95.63 to 105.64%, respectively.