Fluorescent Nanoprobe Research Articles

Fluorescent Nanoprobe Utilizing Tryptophan-Functionalized Silver Nanoclusters for Enhanced Gemcitabine Detection: Optimization and Application in Real Samples

Fluorescent Nanoprobe Utilizing Tryptophan-Functionalized Silver Nanoclusters for Enhanced Gemcitabine Detection: Optimization and Application in Real Samples

Rapid microwave fabrication of highly luminescent nitrogen and phosphorous co-doped carbon quantum dots for the determination of glutathione in pharmaceutical supplements

A facile and sensitive nano-probe for spectrofluorometric glutathione (GSH) determination has been developed based on dual-doped nitrogen and phosphorus carbon quantum dots (NP@CQDs). The NP@CQDs were prepared, through a rapid, one-step microwave heating method in only 180 s with a high quantum yield (0.63) using ethylenediaminetetraacetic acid as carbon and nitrogen precursor and diammonium hydrogen phosphate as nitrogen and phosphorus dopant. The synthesised NP@CQDs had a maximum bluish fluorescence emission at 420 nm, after excitation at 360 nm. The luminescence of the prepared NP@CQDs was quenched via a static quenching mechanism by ferrous ions, while ferric ions did not affect the emission of NP@CQDs. GSH was mixed with ferric ions before adding NP@CQDs to exploit this observation. The attenuation in emission observed after adding NP@CQDs to GSH/ferric ions was directly related to the GSH concentration, as GSH worked to reduce the ferric ions present and produce ferrous ions. The proposed fluorometric method was validated in compliance with the International Council on Harmonization (ICH) guidelines. The proposed fluorescent nano-probe showed good linearity for GSH determination over a range of 0.5–10 µg/mL with % recoveries ranging between 99.50 and 101.86 %, and RSD less than 2 %. NP@CQDs were implemented for GSH determination in pharmaceutical supplementary capsules with respectable accuracy and precision. This approach is simple, reliable, accurate, specific, and it also does not require expensive chemicals or sophisticated equipment. This work opens up other uses of NP@CQDs in pharmaceutical and environmental analysis.

Water-Soluble Photoluminescent Ag Nanoclusters Stabilized by Amphiphilic Copolymers as Nanoprobe for Hypochlorite Detection

Luminescent Ag nanoclusters (Ag NCs) are a promising probe material for sensing and bioimaging applications. However, the intrinsic obstacle of poor water stability and photostability greatly restrict their practical application in biological systems. Herein, we report the intracellular hypochlorite (ClO−) detection with amphiphilic copolymer-modified luminescent Ag NCs with good biocompatibility and photostability. The Ag NCs were synthesized by using chemically inert hydrophobic ligands and then modified with an amphiphilic (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(poly(ethylene glycol))-2000]) (DSPE-PEG-2000) and sodium dodecyl sulfonate (SDS) for phase transfer. It was found that the approach of the removal of organic solvents during the phase transfer has remarkable influences on the properties of the Ag NCs, including their size, luminescence property, and aqueous stability. Furthermore, the silver core of Ag NCs could be oxidatively damaged by ClO−, thereby causing photoluminescence (PL) quenching. The ClO−-induced PL quenching was specific over the other common reactive oxygen species (ROS) as well as some common interferences. Finally, they have been successfully applied as a fluorescent nanoprobe for detecting exogenous and endogenous ClO− in living cells.

Multi-deformable interpenetrating network thermosensitive hydrogel fluorescent device for real-time and visual detection of nitrite

Functionalized thermosensitive hydrogel materials exhibit excellent properties for the fabrication of sensing devices that enable real-time visual detection of food safety duo to their good plasticity and powerful loading capacity. Here, a ratiometric fluorescent device based on an interpenetrating network (IPN) thermosensitive hydrogel was designed to embed functionalized Au nanoclusters (Au NCs) and Blue Carbon dots (BCDs) composites in a multi-network structure to build a sensitive hazardous material nitrite (NO2-) chemsensor. The hydrogel was utilized poloxamer 407 (P407), lignin and cellulose to form stable IPN structure, which resulted in complementation and synergy, thereby strengthening its porous network structure. The combination of fluorescent nanoprobes with the porous network structure has the potential to enhance stable fluorescence signals and improve sensing sensitivity. Moreover, the thermosensitive liquid-solid transition characteristics of the hydrogel facilitate its preparation into diverse sensing devices following curing at room temperature. The hydrogel device, when combined with a smartphone system, converted image information into data information, thereby enabling the accurate quantification of NO2- with a detection limit of 9.38 nM in 2 s. The designed multi-functional hydrogel device is capable of real-time differentiation of NO2- dosage with the naked eye, offering a high-contrast, rapid-response sensing methodology for visual assessment of food freshness. This research contributes to the expansion of hydrogel materials applications and the detection of hazardous materials in food safety.

Dual excitation channel ratiometric fluorescent probes for visual and fluorescent detection of anthrax spore biomarker and tetracycline hydrochloride

Long-term and excessive use of tetracycline hydrochloride (TC) can lead to its accumulation in the environment, which can cause water contamination, bacterial resistance, and food safety problems. 2,6-Pyridine dicarboxylic acid (DPA) is a major biomarker of Bacillus anthracis spores, and its rapid and sensitive detection is of great significance for disease prevention and counter-terrorism. A bifunctional ratiometric fluorescent nanoprobe has been fabricated to detect DPA and TC. 3,5-dicarboxyphenylboronic acid (BOP) was intercalated into layered europium hydroxide (LEuH) by the ion-exchange method and exfoliated into nanosheets as a fluorescent nanoprobe (PNP). DPA and TC could significantly enhance the red fluorescence of Eu3+ through the antenna effect under different excitation wavelengths, while the fluorescence of BOP can be used as a reference based on the constant emission intensity, realizing ratiometric detection. A low limit of detection (LOD) for the target (DPA: 9.7 nM, TC: 21.9 nM) can be achieved. In addition, visual detection of DPA and TC was realized using color recognition software based on the obvious color changes. This is the first ratiometric fluorescent nanoprobe based on layered rare-earth hydroxide (LRH) for the detection of DPA and TC simultaneously, which opens new ideas in the design of multifunctional probes.

A Polymethionine Nanoparticle Fluorescent Probe for Sensitive Detection of Naringin and Naringenin.

In this work, we demonstrated a novel, sensitive and effective fluorescent naringin (NRG) and naringenin (NRGe) detection method using polymethionine nanoparticles (PMNPs) as a fluorescent nanoprobe. The PMNPs were first synthesized by autopolymerization of methionine at 90 °C when trace copper ions existed. The as-prepared PMNPs were thoroughly characterized by transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), gel permeation chromatograph (GPC), nuclear magnetic resonance spectroscopy (NMR), transient and steady-state fluorescence and UV-Vis absorption spectroscopy. The quenching mechanism was attributed to the inner filter effect (IFE). Moreover, the developed assay was used successfully to detect NRG and NRGe in real samples of citrus fruits, illustrating that this detection method has great potential application in the field of citrus fruits analysis.

A self-assembled nanoprobe for rapid detection of hypochlorite in pure water and its application in living cells, food and environmental systems

As an important ROS species participating in various physiological and pathological processes, high level of hypochlorite (ClO−) poses significant health and safety concerns, necessitating efficient detection methods. Herein, this study introduces a water-soluble fluorescent nanoprobe Nano-SJD, effectively detect ClO− in both food samples and living cells. The small molecular probe SJD with N, N-dimethylthiocarbamyl (DMTC) as recognition moiety was constructed based on a naphthalene derivative. To further improve the water solubility, SJD was assembled with an amphiphilic copolymer (mPEG-DSPE) to prepare a water soluble fluorescent nanoprobe Nano-SJD. Fortunately, the nanoprobe preserves the excellent properties of small molecules and performs very well optical response to ClO− in aqueous solution, possessing the advantages including ultra-rapid response (within 1 s), minimal interference, low detection limits (0.39 μM) and good pH stability. What's more important, we have also developed smartphone-compatible test paper strips for convenient on-site detection of ClO− in real-water samples. Additionally, the robust fluorescent imaging behavior of Nano-SJD for visualization of ClO− in living cells highlights its broad potential in biosystem applicability.

A novel ratiometric fluorescent nanoprobe based on “antenna effect” for discriminating leucine enantiomers

D-Leucine is a potential biomarker for diagnosing diabetes, therefore detection of D-Leu and discrimination of Leu enantiomers are of great importance. Herein, a new fluorescent nanosensor Eu-DLSiNPs was synthesized at room temperature. Based on the “antenna effect”, a chiral ratiometric fluorescent nanoprobe Eu-DLSiNPs/OTC was obtained by simple mixing with oxytetracycline (OTC). This new sensing system showed two distinctive emission peaks at 480 nm and 616 nm, respectively. The addition of D-Leu can cause the fluorescence intensity decreased at 480 nm and enhanced at 616 nm, while L-Leu has no significant effect on the emission of the nanoprobe, so the ratiometric discrimination of Leu enantiomers can be realized. The mechanism of the enantiomeric fluorescence recognition was systematically studied. This work provides a new strategy for the recognition of leucine enantiomers and will paved a new way for discriminating other important chiral compounds.

Fluorescent MnO2@DEHP Nanoprobe for Rapid and Selective Detection of Fe(III) ions.

Particle extraction via the liquid-liquid interface (PELLI) method has been utilized to produce Di-(2-ethylhexyl) phosphate (DEHP) coated MnO2 fluorescent nanoprobe denoted as MnO2@DEHP for the selective detection of Fe3+ ions. The synthesized MnO2@DEHP nanoprobe was characterized by various instrumental techniques such as FT-IR, PXRD, TEM, EDAX, HRTEM, DLS, and XPS. Since the high concentration of Fe3+ in waste water leads to water pollution, which in turn affects the ecosystem, and causes severe health hazards. Therefore, accurate detection of Fe3+ ions in the aqueous systems is essential as they are involved in various chemical and biological processes in living things. Here, the synthesized MnO2@DEHP nanoprobe selectively detects Fe3+ ions in the presence of various metal ions in an aqueous media by fluorescence quenching (turn-off) mechanism. The limit of detection (LOD) of MnO2@DEHP nanoprobe for Fe3+ was found to be 0.49µM. The test-strip method and real water sample analysis were also used to demonstrate the viability of MnO2@DEHP as a fluorescent nanoprobe to detect Fe3+ ions visually and in environment monitoring applications.

A luminescent metal–organic framework composite as a turn-on sensor for the selective determination of monosodium glutamate in instant noodles

This work reports the development and application of a new fluorescent nanoprobe sensor depending on using luminescent metal organic framework (LMOF). The developed sensor composed of hybridized Ca 1,3,5-benzenetricarboxylic acid metal organic framework with microcrystalline cellulose (Ca-BTC/MCC MOF) as a fluorescent probe for the determination of the monosodium glutamate (MSG), a non-chromophoric food additive. The developed sensor was characterized using a high-resolution scanning electron microscope (HR-SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The Ca-BTC/MCC MOF hybrid, examined under the HR-SEM, showed morphological features different from the MCC and the Ca-BTC MOF. The diffraction patterns of Ca-BTC/MCC composites clearly displayed the characteristic Ca-BTC MOF diffraction bands, indicating that MCC was successfully incorporated in the formation of crystalline MOF hybrids. The FTIR spectra show the bands of MCC, as well as the bands of Ca-BTC MOFs. The prepared nanoprobe was successfully applied as a sensitive sensor for the determination of MSG in food sample. The method was validated following the International ICH (Q2)R2 guidelines in terms of precision, trueness and other main analytical figures of merit, comprised the green profile and practicability metrics. A wide linearity range was achieved (5–50 µg/mL) with good correlation coefficient (R2 ≥ 0.9993). The recoveries (%) were found in the range of 100.0 to 101.5 and the RSDs (%) were in the range of 0.1 to 0.9 %.These results show that the developed nanoprobe was selective, and highly accurate to determine this important food additive in the seasonings of instant noodles, also showing a reduced environmental impact based on the metrics currently accepted for the evaluation of the green profile and practicability.

Wearable, Biocompatible, and Dual-Emission Ocular Multisensor Patch for Continuous Profiling of Fluoroquinolone Antibiotics in Tears.

The abuse or misuse of antibiotics in clinical and agricultural settings severely endangers human health and ecosystems, which has raised profound concerns for public health worldwide. Trace detection and reliable discrimination of commonly used fluoroquinolone (FQ) antibiotics and their analogues have consequently become urgent to guide the rational use of antibiotic medicines and deliver efficient treatments for associated diseases. Herein, we report a wearable eye patch integrated with a quadruplex nanosensor chip for noninvasive detection and discrimination of primary FQ antibiotics in tears during routine eyedrop treatment. A set of dual-mode fluorescent nanoprobes of red- or green-emitting CdTe quantum dots integrated with lanthanide ions and a sensitizer, adenosine monophosphate, were constructed to provide an enhanced fluorescence up to 45-fold and nanomolar sensitivity toward major FQs owing to the aggregation-regulated antenna effect. The aggregation-driven, CdTe-Ln(III)-based microfluidic sensor chip is highly specific to FQ antibiotics against other non-FQ counterparts or biomolecular interfering species and is able to accurately discriminate nine types of FQ or non-FQ eyedrop suspensions using linear discriminant analysis. The prototyped wearable sensing detector has proven to be biocompatible and nontoxic to human tissues, which integrates the entire optical imaging modules into a miniaturized, smartphone-based platform for field use and reduces the overall assay time to ∼5 min. The practicability of the wearable eye patch was demonstrated through accurate quantification of antibiotics in a bactericidal event and the continuous profiling of FQ residues in tears after using a typical prescription antibiotic eyedrop. This technology provides a useful supplement to the toolbox for on-site and real-time examination and regulation of inappropriate daily drug use that might potentially lead to long-term antibiotic abuse and has great implications in advancing personal healthcare techniques for the regulation of daily medication therapy.

N-rich carbon nanosphere as fluorescent nanoprobe for intracellular iron

Nitrogen rich carbon nanoparticles are known to provide higher fluorescence stokes shift, and thereby are potential candidates for fluorescent sensors. Herein, a facile one-step hydrothermal synthesis is reported for N-rich carbon nanospheres (G-CNS) from caffeine and o-phenylenediamine as precursors. The as-synthesized G-CNS showed high fluorescence with λem at 509 nm, with a highly selective fluorescence turn-off response towards Fe2+/Fe3+, rendering these carbon nanospheres as potential candidates to detect intracellular labile iron pool in live cells. The intracellular labile iron pool in iron-overloaded cells was sensed using the synthesized G-CNS. Mechanistically, the fluorescence quenching via dynamic pathway involves the formation of an excited state charge transfer process, which undergoes non-radiative decay.

A Ratiometric Fluorescence Probe Based on Silver Nanoclusters and CdSe/ZnS Quantum dots for the Detection of Hydrogen Peroxide by Aggregation and Etching.

In this study, a ratiometric fluorescence nanoprobe is developed for the analysis of hydrogen peroxide (H2O2). Silver nanoclusters (AgNCs) were synthesized by chemical reduction method using sodium borohydride (NaBH4) as reducing agent, and were coupled with CdSe/ZnS quantum dots (QDs) to form the ratiometric fluorescence nanoprobe silver nanoclusters-quantum dots (AgNCs-QDs). The effect of the volume ratio of CdSe/ZnS QDs to AgNCs on the fluorescence ratio of AgNCs-QDs was investigated. The fluorescence characterization results show that two emission peaks of AgNCs-QDs are located at 473nm and 661nm, respectively. Transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) results show that H2O2 can cause the fluorescence probe to aggregate, while etching AgNCs to produce silver ions, which together cause the fluorescence of the QDs in the ratiometric fluorescent probe to be quenched. Based on this strategy, the fluorescence intensity ratio of the two emission peaks F473/F661 exhibits a strong linear correlation with the concentration of H2O2. The detection range is 3.32 µM ~ 2.65 mM with a detection limit of 3.32 µM. In addition, the ratiometric fluorescence probe can specifically recognize H2O2 and has excellent anti-interference performance and good fluorescence stability. Importantly, the probe was utilized for the detection of H2O2 in serum, showing the possibility of the probe in clinical detection applications.

Injectable and Sprayable Fluorescent Nanoprobe for Rapid Real-Time Detection of Human Colorectal Tumors.

The development of minimally invasive surgery has greatly advanced precision tumor surgery, but sometime suffers from restricted visualization of the surgical field, especially during the removal of abdominal tumors. A 3-D inspection of tumors could be achieved by intravenously injecting tumor-selective fluorescent probes, whereas most of which are unable to instantly distinguish tumors via in situ spraying, which is urgently needed in the process of surgery in a convenient manner. In this study, this work has designed an injectable and sprayable fluorescent nanoprobe, termed Poly-g-BAT, to realize rapid tumor imaging in freshly dissected human colorectal tumors and animal models. Mechanistically, the incorporation of γ-glutamyl group facilitates the rapid internalization of Poly-g-BAT, and these internalized nanoprobes can be subsequently activated by intracellular NAD(P)H: quinone oxidoreductase-1 to release near-infrared fluorophores. As a result, Poly-g-BAT can achieve a superior tumor-to-normal ratio (TNR) up to 12.3 and enable a fast visualization (3min after in situ spraying) of tumor boundaries in the xenograft tumor models, Apcmin/+ mice models and fresh human tumor tissues. In addition, Poly-g-BAT is capable of identifying minimal premalignant lesions via intravenous injection.

A programmable sensitive platform for pathogen detection based on CRISPR/Cas12a -hybridization chain reaction-poly T-Cu

Rapid and sensitive detection of pathogenic bacteria is crucial for disease prevention and control. The CRISPR/Cas12a system with the DNA cleavage capability holds promise in pathogenic bacteria diagnosis. However, the sensitivity of CRISPR-based assays remains a challenge. Herein, we report a versatile and sensitive pathogen sensing platform (HTCas12a) based on the CRISPR/Cas12a system, hybridization chain reaction (HCR) and Poly T-copper fluorescence nanoprobe. The sensitivity is improved by HCR and the Poly-T-Cu reporter probe reduces the overall experiment cost to less than one dollar per sample. Our results demonstrate the specific recognition of target nucleic acid fragments from other pathogens. Furthermore, a good linear correlation between fluorescence intensity and target quantities were achieved with detection limits of 23.36 fM for Target DNA and 4.17 CFU/mL for S.aureus, respectively. The HTCas12a system offers a universal platform for pathogen detection in various fields, including environmental monitoring, clinical diagnosis, and food safety.

Rational Design of Activatable Lanthanide NIR-IIb Emissive Nanoprobe for In Situ Specific Imaging of HOCl In Vivo.

Hypochlorous acid (HOCl), as an indispensable signaling molecule in organisms, is one of the key members of reactive oxygen species (ROS). However, in vivo, real-time dynamic near-infrared fluorescence imaging of HOCl levels in the 1400-1700nm sub-window (NIR-IIb) remains a major challenge due to the lack of suitable detection methods. Herein, a general design of HOCl-responsive NIR-IIb fluorescence nanoprobe is proposed by integrating NaLuF4Yb/Er@NaLuF4 downshift nanoparticles (DSNPs) and HOCl recognition/NIR-IIb emissive modulation unit of M2-xS (M = Cu, Co, Pb) nanodots for real-time monitoring of HOCl levels. The fluorescence modulation unit of M2-xS nanodots presents remarkably enhanced absorption than Yb sensitizer at 980nm and greatly inhibits the NIR-IIb fluorescence emission via competitive absorption mechanism. While, the M2-xS nanodots are easily degraded after triggering by HOCl, resulting in HOCl responsive turn-on (≈ten folds) NIR-IIb emission at 1532nm. More importantly, in vivo highly precise and specific monitoring of inflammatory with abnormal HOCl expression is successfully achieved. Thus, the explored competitive absorption mediated quenching-activation mechanism provides a new general strategy of designing HOCl-responsive NIR-IIb fluorescence nanoprobe for highly specific and sensitive HOCl detection.

Redox-responsive degradation of DNA@MnO2 nanoprobe triggering DNAzyme recycling amplification for sensitive and label-free detection of glutathione

In this work, a novel fluorescence nanoprobe based on MnO2 nanosheets and DNAzyme cyclic amplification was developed for label-free detection of GSH. In our design, the DNA@MnO2 nanoprobe was facilely prepared through the adsorption of DNA probes on the surface of MnO2 nanosheets. Importantly, MnO2 nanosheets in the DNA@MnO2 nanoprobe can act as the recognizer of analytical target GSH. In the presence of GSH, the DNA@MnO2 nanoprobe are decomposed owing to redox-responsive reaction between GSH and MnO2 nanosheets, resulting in the generation of abundant Mn2+ and the desorption of DNA probes. Subsequently, the Mn2+-dependent DNAzyme recycling amplification was rapidly initiated and a large number of the blocked G-rich sequences in DNA probes was released. The G-rich sequences were efficiently folded into G-quadruplex structures, which can remarkably light up the fluorescence intensity of thioflavin T (ThT). Experimental data demonstrated that the DNA@MnO2 nanoprobes for GSH detection have a wide linear range from 0 to 2000 µM. Moreover, this fluorescence sensing strategy was successfully applied for the detection of GSH in complex biological media with satisfying results, providing a simple, facile and cost-efficient nanoplatform for GSH-related clinical disease diagnosis.

Magneto-fluorescent nanobiosensor with tetrahedral framework nucleic acid-confined aptamer for trace adenosine triphosphate detection

Accurate quantitation of trace-level ATP biomarkers often suffers from interference of sample matrix and remains a challenge. Herein, a novel magnetic biological nanosensor (MBNS) integrating tetrahedral framework nucleic acid (tFNA)-confined aptamers and ultrasensitive laser-induced fluorescence (LIF) was tailored and evaluated. The fluorescent aptamer nanoprobe hybridized with FAM-labelled cDNA was particularly incorporated into the inner cavity of tFNA, enabling a dual-mode mechanism that integrates molecular size selection and aptamer affinity recognition. By this strategy, the benefits of tFNA molecular sieve, the super sensitive properties of LIF, and the specific recognition of “aptamer gene codes” were integrated, as triggered the superior response of ATP. The structures, properties and reaction mechanism of tFNA, as well as tFNA modified with aptamer probe at different sites, were characterized in detail. A high level of anti-interference was achieved, shielding against non-specific adsorption even in matrices with high protein and analogue content, 103∼105 times higher than ATP. The release of fluorescent beacon from aptamer probe was facilely driven by specific binding of ATP, and an ultra-sensitive detection of 75 pmol/L ATP was obtained without amplification. It was 2–3 orders of magnitude more sensitive than most fluorescent aptasensors. Applied to serum samples, the stability and reproducibility of the resultant aptasensor have been validated with the intra- and inter-assay RSD in 1.6–6.4 % and -1.5–8.4 %, respectively. Acceptable recoveries of 96.5–106.8 % were achieved, consistent with the LC-MS method. It was expected to open a simple and efficient protocol for highly specific and ultrasensitive ATP detection in clinical diagnostics.

Lignocellulosic biomass-derived carbon quantum dots (CQDs): A novel approach utilizing organosolv lignin from Moso bamboo waste

Converting lignocellulosic materials to carbon quantum dots (CQDs) has garnered significant interest to transform biomass wastes into highly valuable products. We chose to use lignin as our feedstock because high-value products more readily utilize cellulose and hemicellulose. Lignin, arguably the most underutilized and complex biopolymer within any biomass, presents an appealing yet overlooked opportunity. While some may argue that lignin-based CQDs are no longer groundbreaking, this is because existing studies typically rely on commercially available lignin, ignoring biomass-derived sources. Therefore, in our pioneering research, we utilized organosolv lignin, prized for its structural purity and extracted from Moso bamboo waste, as the carbon source in a facile two-step technique to synthesize luminous CQDs. The process involved the addition of 2,4-diaminobenzenesulfonic acid, a mild-organic acid that acted as a source for both nitrogen (N) and sulphur (S). A 12-h hydrothermal treatment at 200 °C with 0.1 M of acid addition attained the best result. The resultant CQDs display strong green fluorescence, with the highest quantum yield of 17.7% seen in N and S co-doped CQDs. With their obvious and specific fluorescence quenching impact on Fe3+, CQDs demonstrate great potential as a fluorescent nanoprobe for metal ion detection. This CQD nanoprobe responds very sensitively to Fe3+ between 0 and 500 μM (R2 = 0.9803), with a detection limit of 0.15 μM. This research not only presents a unique alternative nanoprobe for the sensing field using renewable biomass lignin, but it also paves the way for the long-term, cost-effective, and scalable manufacturing of CQDs.

Quantification and visualization of penicillin G residues in milk using a ratiometric fluorescent nanoprobe based on carbon dots and gold nanoclusters

Developing an effective assay for monitoring penicillin G (PNG) is important for safeguarding ensuring public health and food safety. This work details the application of carbon dots (CDs) emitting blue light and gold nanoclusters (GNCs) with red emission as ratiometric fluorescence (RF) probes for the sensitive detection of PNG. The RF probe under a single excitation of 360 nm wavelength displayed two discrete emission peaks at 444 and 660 nm related to CDs and GNCs, respectively. Following the introduction of PNG, the red fluorescence intensity of GNCs was found to be reduced through the inner filter effect (IFE); meanwhile, the blue fluorescence of CDs remained unchanged under optimal conditions. The quantification of PNG can be achieved by this RF nanoprobe by following the I660/I444 ratio in two ranges of 0.1–0.8 ppm and 0.8–30.0 ppm and with a limit of detection (LOD) as low as 30 ppb. Furthermore, the RF probe has been successfully employed to determine PNG in milk samples with acceptable recoveries and results were validated by HPLC. Finally, the visual capability of this RF probe can greatly enhance and facilitate on-site determination process of PNG.