Ratiometric Fluorescent Nanosensor Research Articles

A novel ratiometric fluorescent nanosensor based-on UiO-66-NH2 capped carbon dots for nitrite determination

Nitrite is a commonly used food preservative and a water contaminant that has garnered significant attention due to its harmful effects on human health. Developing a simple and sensitive method for determining nitrite levels is crucial for safeguarding public health. In this paper, we present a novel ratiometric fluorescent nanosensor (CDs@UiO-66-NH2), created by combining orange-red-emitting CDs with blue-emitting UiO-66-NH2. This ratiometric probe detects nitrite ions (NO2−) based on the diazotization reaction between the amino group in UiO-66-NH2 and the target NO2−, where the blue emission of UiO-66-NH2 is quenched but the orange-red emission of CDs remains stable. The probe demonstrated a detection range of 0.5–20 μM with a limit of detection (LOD) of 0.157 μM for NO2−. Due to the probe’s distinct color changes in response to NO2−, RGB values can be easily read using a smartphone, enabling ultrasensitive visual detection of NO2− with an LOD of 0.76 μM. This sensor was successfully applied to detect NO2− in environmental water samples. Finally, a smartphone-based RGB reading method using CDs@UiO-66-NH2 for visual quantitative detection of NO2− was proposed, broadening the application of CDs@UiO-66-NH2 in environmental protection.

Exposure to nanoplastics induces the elevation of Zn2+ levels in cells as visualized by a Golgi apparatus-targetable ratiometric fluorescent nanosensor

Nanoplastics are prevalent in the environment and emerging evidence suggests they can induce organ injury by activating oxidative stress. Given that both nanoplastics and Zn2+ levels are intertwined with oxidative stress, it is crucial to investigate the influence of nanoplastics on the level of labile Zn2+ and get a better understanding of their cytotoxicity mechanisms. At the organelle level, the Golgi apparatus plays an active role in stress responses. In this study, we synthesized Golgi-Zn, the first ratiometric fluorescence nanosensor with Golgi apparatus targeting ability for monitoring of Zn2+. This nanosensor demonstrated high sensitivity and selectivity as well as robust pH stability for Zn2+ sensing. The ratio of the two fluorescence signals of Golgi-Zn showed a good linearity with Zn2+ concentration in the range of 0.5–10 μM, achieving a limit of detection of ∼72.4 nM. Furthermore, the nanosensor exhibited low cytotoxicity and effectively targeted the Golgi apparatus. Leveraging these fascinating features, we successfully applied Golgi-Zn for visualizing exogenous and endogenous Zn2+ levels in the Golgi apparatus. Moreover, with the help of Golgi-Zn, we found that nanoplastics stimulation could increase the level of Zn2+ in the Golgi apparatus.

Gold nanoclusters and amino-modified mesoporous silica-encapsulated carbon dot fluorescence nanosensors combined with LightGBM algorithm for ultra-fast detection of Co2+

In this study, we develop a novel ratiometric fluorescent nanosensor for the detection excess Co2+ in soil. This fluorescent nanosensor is fabricated using mesoporous silica-encapsulated nitrogen-doped carbon dots (N-CDs@mSiO2) and gold nanoclusters stabilized by bovine serum albumin (BSA-AuNCs). The green fluorescence of the carbon dots within the mesoporous silica spheres (mSiO2) serves as an internal reference signal. The red fluoresence BSA-AuNCs are covalently connected onto the surface of amino-functionalized nanospheres (N-CDs@mSiO2-NH2), providing the response signal. This nanosensor has dual emission peaks at 520 nm and 650 nm under excitation wavelength of 380 nm. The addition of Co2+ to this nanosensor causes the fluorescence quenching at 650 nm while the green fluorescence at 520 nm remains unchanged, resulting in fluorescence color change from yellow to green. The developed ratiometric fluorescence nanosensor exhibits excellent selectivity to Co2+ with a range of 2.00–200.00 μM and a detection limit as low as 0.74 μM. In addition, a Co2+ prediction model is developed using the Light Gradient Boosting Machine (LightGBM) algorithm. The entire detection process is within 10 s and the model prediction value is as high as 0.991 on average. This shows that the proposed fluorescent nanosensor, optimized with the LightGBM algorithm, provides an efficient, environmentally friendly and potentially practical solution for Co2+ detection.

Highly sensitive and selective detection of amoxicillin using molecularly imprinted ratiometric fluorescent nanosensor based on quantum dots.

A dual-emission ratiometric fluorescence sensor (CDs@CdTe@MIP) with a self-calibration function was successfully constructed for AMO detection. In the CDs@CdTe@MIP system, non-imprinted polymer-coated CDs and molecule-imprinted polymer-coated CdTe quantum dots were used as the reference signal and response elements, respectively. The added AMO quenched the fluorescence of the CdTe quantum dots, whereas the fluorescence intensity of the CDs remained almost unchanged. The AMO concentration was monitored using the fluorescence intensity ratio (log(I647/I465)0/(I647/I465)) to reduce interference from the testing environment. The sensor with a low detection limit of 0.15μg/L enableddetection ofthe AMO concentration within 6min. The ratiometric fluorescence sensor was used to detect AMO in spiked pork samples; it exhibited a high recovery efficiency and relative standard deviation (RSD) of 97.94-103.70% and 3.77-4.37%, respectively. The proposed highly sensitive and selective platform opens avenues for sensitive, reliable, and rapid determination of pharmaceuticals in the environment and food safety monitoring using ratiometric sensors.

A ratiometric and selective fluorescent nanosensor for determining Hg2+ ions based on a novel functionalized metal–organic framework

A new method using fluorescence was developed to detect Hg2+ ions in water. This method relied on the reaction between NH2‐MIL‐53(Al) and 5‐bromo‐2‐hydroxyacetophenone. The method was carefully fine‐tuned for optimal reaction conditions and analytical parameters like pH levels, nanosensor quantity, and detection limits. It showed great linearity in detecting Hg2+ ions in the range of 0.0–3.0 ppm (0.0–1.50 × 10−5 M), with a very low detection limit of 1.65 × 10−2 ppm (8.23 × 10−8 M). We tested how well the method can distinguish between different substances by investigating whether other common substances in water samples would interfere. The results were positive, as the presence of these substances did not significantly affect the accuracy of detecting Hg2+ ions, confirming the method's reliability. In order to confirm its dependability, we conducted a quantitative test to detect Hg2+ ions in water samples. The recovery rates obtained ranged from 97.16% to 103.2%, demonstrating the method's precision and accuracy. A comparison with inductively coupled plasma optical emission spectrometry (ICP‐OES), a well‐known method for analyzing trace metals, produced similar results, further instilling confidence in the 5Br2HA = N‐Al‐MOF nanosensor that was developed. In general, this research emphasizes the exciting potential of the new nanosensor in detecting Hg2+ ions in various water and cosmetic samples. It provides a strong and dependable alternative to traditional detection methods.

Molecular Imprinting-Based Ratiometric Fluorescence Nanosensor and Kit for Rapid and Visual Detection of Folic Acid

Molecular Imprinting-Based Ratiometric Fluorescence Nanosensor and Kit for Rapid and Visual Detection of Folic Acid

Sleep deprivation boosts O2·- levels in the brains of mice as visualized by a Golgi apparatus-targeted ratiometric fluorescence nanosensor.

Sleep deprivation (SD) is highly prevalent in the modern technological world. Emerging evidence shows that sleep deprivation is associated with oxidative stress. At the organelle level, the Golgi apparatus actively participates in the stress response. In this study, to determine whether SD and Golgi apparatus stress are correlated, we rationally designed and fabricated a novel Golgi apparatus-targeted ratiometric nanoprobe called Golgi dots for O2·- detection. This probe exhibits high sensitivity and selectivity in cells and brain slices of sleep-deprived mice. Golgi dots can be readily synthesized by coprecipitation of Golgi-F127, an amphiphilic polymer F127 modified with a Golgi apparatus targeting moiety, caffeic acid (CA), the responsive unit for O2·-, and red emissive carbon nanodots (CDs), which act as the reference signal. The fluorescence emission spectrum of the developed nanoprobe showed an intense peak at 674nm, accompanied by a shoulder peak at 485nm. As O2·- was gradually added, the fluorescence at 485nm continuously increased; in contrast, the emission intensity at 674nm assigned to the CDs remained constant, resulting in the ratiometric sensing of O2·-. The present ratiometric nanoprobe showed high selectivity for O2·- monitoring due to the specific recognition of O2·- by CA. Moreover, the Golgi dots exhibited good linearity with respect to the O2·- concentration within 5 to 40μM, and the limit of detection (LOD) was ~ 0.13μM. Additionally, the Golgi dots showed low cytotoxicity and an ability to target the Golgi apparatus. Inspired by these excellent properties, we then applied the Golgi dots to successfully monitor exogenous and endogenous O2·- levels within the Golgi apparatus. Importantly, with the help of Golgi dots, we determined that SD substantially elevated O2·- levels in the brain.

A ratiometric fluorescence nanosensor for glutathione detection based on spatially confined dual-emission of α-lipoic acid-modified gold nanoclusters and silicon nanoparticles.

The development of dual-emission ratiometric fluorescent probes with aggregation-induced emission enhancement (AIEE) overcomes the limitations of gold nanocluster (Au NC)-based probes, particularly their weak intrinsic fluorescence, in real-world applications. These AIEE probes also exhibit superior detection limits and enhanced sensitivity. A novel combination for the reliable fluorometric detection of glutathione (GSH) was proposed, utilizing aggregation-induced emission enhancement (AIEE) facilitated by electrostatic interaction and spatial confinement. The probe consists of a ratiometric combination of negatively charged α-lipoic acid-modified Au NCs (LA@Au NCs) and positively charged silicon nanoparticles (SiNPs). The addition of SiNPs causes aggregation of LA@Au NCs, enhancing the fluorescence of LA@Au NCs through the AIE effect under electrostatic interaction and spatial confinement. The addition of Cu2+ quenched the emission of LA@Au NCs as a result of charge transfer. The fluorescence emissions of LA@Au NCs were restored upon the addition of GSH due to the interaction between GSH and Cu2+. Simultaneously, the emission signal of SiNPs remains unchanged, serving as an internal reference signal during GSH measurement. It was found that the fluorescence ratio (F680/F465) is directly proportional to the concentration of GSH in the range of 0.05-100 μM, with a detection limit of 1.7 nM (S/N = 3). The proposed system was applied to detect GSH in real samples, including dietary supplements, human serum, and saliva samples. This work opens new avenues for constructing novel sensors based on AIEE for detecting biomolecules.

High dispersibility ratiometric fluorescence sensor designed by functionalized mesoporous silica nanopraticles for sensing and imaging of hydrogen peroxide

Herein, a mesoporous silica nanoparticle (MSN) based ratiometric fluorescence nanosensor (MSN-BA-SiCD) with improved performance was designed for monitoring hydrogen peroxide (H2O2). Specifically, H2O2 response molecule (BA) with AIE feature was synthesized and encapsulated into MSN channel as the fluoresent recognition site. Afterwards, silane-modified carbon dot (SiCD) was covalently connected to the MSN surface which can effectively prevent the leakage of BA and improve the water dispersibility of the nanosensor. The presence of H2O2 could result in a “turn-on” fluorescence of BA as well as concurrent variation in the fluorescence resonance energy transfer (FRET) signal between SiCD and BA. MSN-BA-SiCD displays a specific blue-to-green resolved emission change in response to H2O2 and the detection limit can be as low as 4.78 × 10−6 M. In addition, the nanosensor exhibited enhanced photostability due to the protection of the material framework. Moreover, the nanosensing system was successfully applied to detect H2O2 in beer, orange juice and living cells. The excellent water dispersibility and photostability of the nanosensor, together with high specificity and biocompatibility, constituted an advanced set of characteristics among existing MSNs, which was expected to further promote the development of H2O2 sensors in the environmental and biological fields.

Visualized time-temperature monitoring by triplet-sensitized ratiometric fluorescent nanosensors

Time-temperature indicators (TTIs) with the capability to visually reflect the accumulated time and temperature effect for real time are of substantial significance for securing the safety and quality of perishable products, such as foods and medical products. Herein, we design a novel TTI with high accuracy and low cost based on a ratiometric fluorescent nanosensor capable of self-calibration. The nanosensor was fabricated via the co-assembly of amphiphilic block copolymer and a responsive triplet-triplet annihilation upconversion (TTA-UC) system. The pH responsiveness of the triplet-sensitized nanomicelle was well investigated experimentally and theoretically. A linear relationship between the intensity ratio (of the integrated upconversion emission to the integrated phosphorescence emission) and pH was revealed for the ratiometric fluorescent nanomicelle. The TTA-UC functionalized nanomicelle turned out to be an extraordinary nanosensor with excellent sensitivity, reliability, and anti-reference. Subsequently, the nanomicelle was firstly applied for enzymatic time-temperature indicators (TTIs). Comprehensive kinetic study of the TTI prototype and the released total volatile basic nitrogen during meat storage was conducted under isothermal and non-isothermal conditions, which demonstrated remarkable correlation between the TTI response and the food spoilage. The activation energy of the TTI prototype could be readily modified to satisfy diverse food products including meat, diary, and aquatic products. The TTI based on triplet-sensitized ratiometric fluorescent nanosensor could be employed for visual monitoring food quality with low cost, high accuracy, and good reliability.

A new ratiometric fluorescence nanosensor based on NaYF4:3%Er@NaYF4 upconversion nanoparticles for sensitive determination of Rose Bengal in water

Rose Bengal (RB) is used as a sensitizer in ambient water due to its property of catalyzing the production of singlet oxygen (1O2). However, this property also brings phototoxicity and carcinogenicity. The NaYF4:3%Er@NaYF4 core-shell upconversion nanoparticles (UCNPs) with higher upconversion efficiency was synthesized to detect RB in ambient water. Due to fluorescence resonance energy transfer (FRET) between RB and UCNPs, the upconversion fluorescence at 538 nm emitted by UCNPs was quenched by the RB, while the emission at 566 nm of RB raised. In the best conditions, the ratiometric emission intensity F566/F538 was positively proportional to RB concentration and the linear range was 0.04–15.0 μg·mL−1 (R2 = 0.996). The detection limit (S/N = 3) of RB was 2.46 ng·mL−1. The recoveries ranged from 99.0% to 105.6% (relative standard deviation 0.97–3.24%, n = 3) in tap water and 100.3%–104.9% (relative standard deviation 0.66–1.94%, n = 3) in lake water. This proposed method exhibits lower detection limit and larger linear, which possesses practical application value to the detection of RB in water.

Construction of ratiometric fluorescent nanosensors based on carbon dots dual emission strategy for high-sensitivity visual detection of Ag+

ABSTRACT Water-soluble purple fluorescent carbon nanodots (P-CDs) were synthesised using 2-phenylphenol, and red fluorescent carbon dots (R-CDs) were prepared from o-phenylenediamine and phosphoric acid. Based on the fluorescence quenching effect of Ag+ on carbon quantum dots, and additionally introducing a red light-emitting quantum dot with excellent performance and high quantum yield, a dual emission ratiometric fluorescent nanosensor (P-CDs/R-CDs) was established. The semi-quantitative detection of silver ions can be realised. Under the excitation light of 254 nm and 365 nm, the fluorescence spectrum shows double emission fluorescence peaks at 343 nm and 626 nm, which originate from the fluorescence emission of the synthesised C-dots and the additionally introduced C-dots, respectively. The relationship between the ratio of the intensity of the two emission peaks F343/F626 and the concentration of silver ions realises the analysis and detection of silver ions. The linear detection range of this method was 0.096–10 μM, and the detection limit (LOD, S/N = 3) was 32 nM. In addition, the method can also perform naked-eye visual detection according to the fluorescence colour change of the probe under ultraviolet light, and realise the rapid monitoring of Ag+ on site. The P-CDs/R-CDs ratiometric fluorescence sensor provides a new method for the detection of Ag+ and promotes the development of heavy metal ion sensing.

A dual-emission ratiometric fluorescent biosensor for ultrasensitive detection of glibenclamide using S-CDs/CdS quantum dots

In the present work, sulfide-doped carbon dots (S-CDs)/cadmium sulfide quantum dots (CdS QDs) ratiometric fluorescent nanosensor has been developed for sensitive and selective determination of glibenclamide (GLC) in biological fluids. The method was based on the quenching effect of GLC on the dual-emission intensity of the S-CDs/CdS QDs system at 420 nm and 650 nm, which are related to S-CDs and CdS QDs, respectively. The fluorimetric data analysis indicated that the fluorescence signals of the system were quenched by adding GLC in a concentration-dependent manner. A good linear relationship was observed between GLC concentration and the quenched fluorescence intensity of the S-CDs/CdS QDs in the range of 0.3 nM−10.0 μM. The limit of detection (LOD) value was estimated to be 0.12 nM. Furthermore, under optimum conditions, GLC was detected in spiked human serum sample (as real media) using the developed ratiometric nanosensor with an accuracy of 99.6%. According to the results, the developed dual-emission system can be used as a reliable method for the quantitative detection of GLC in biological samples.

Gold Nanoclusters and Silica-Coated Carbon Dots-Assisted Ratiometric Fluorescent Nanosensors for Ultrasensitive Detection of Glyphosate

In this work, a novel ratiometric fluorescent nanosensor by coupling mesoporous silica spheres-coated nitrogen-doped carbon dots (N-CDs@SiO2) and bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) was developed for sensitive detection of glyphosate. BSA-AuNCs nanocomposites were covalently connected onto the surface of amino-functionalized N-CDs@SiO2 nanospheres, causing the core-satellite probes with two fluorescence emissions at 436 and 651 nm, respectively, under a single excitation of 360 nm. The N-CDs@SiO2@BSA-AuNCs “signal on–off–on” ratiometric fluorescent probes could realize highly selective differentiation and accurate detection of glyphosate based on the fluorescence quenching of Cu2+ on BSA-AuNCs and glyphosate-induced fluorescence recovery due to the strong complexation of glyphosate toward Cu2+. The developed ratiometric fluorescent nanosensor exhibited excellent selectivity to glyphosate, wide detectability in a concentration range of 5–100 ng/mL, high sensitivity with a low detection limit of 3.4 ng/mL, as well as fascinating reliability and practicability in real malt samples with recoveries of 94.81–101.61%. This study provides a universal platform for versatile sensing of more trace analytes in complex matrices and can be extended for wide application in the environment and food safety fields.

A dummy molecularly imprinted ratiometric fluorescence nanosensor for the sensitive detection of guanidyl-microcystins in environmental water.

An effective strategy is proposed to construct a highly sensitive ratiometric fluorescence sensing platform for microcystins (MCs) based on a dummy molecularly imprinted polymer using metformin as a template. The imprinted nanohybrids of carbon dots (CDs) combined with fluorescein isothiocyanate (FITC) are synthesized (CDs-FITC-SiO2@MIP), in which the CDs and FITC serve as assisted response signals and reference enhancement signals, respectively. Metformin can be used as a dummy template for MCs due to its partially similar molecular fragments to MCs that can form a specific recognition site cavity. MCs can simultaneously induce an obvious fluorescence quenching effect for the CDs and a reference fluorescence enhancement for FITC-SiO2, enabling ratiometric fluorescence detection of MCs. Thus, CDs-FITC-SiO2@MIP used as a signal probe has favorable sensitivity, stability, and selectivity. More importantly, a good linear relationship between the fluorescence intensity ratio (I620/450) and the concentration of MCs in the range of 0.5-500 μg L-1 is obtained with a LOD of 0.013 μg L-1 and 0.022 μg L-1 for MC-RR and MC-LR, respectively, under the optimum conditions. This method has great application potential in water quality monitoring by using CDs-FITC-SiO2@MIP as a promising candidate for monitoring MCs in complex systems.

Green ratiometric fluorescent dual-mode nanosensor for highly selective and sensitive detection of new coccine in food

New coccine is one of the most used red colorants in foods. Due to its cytotoxicity, quantitative determination is very necessary. Herein, the ratiometric fluorescent and UV absorption dual-mode nanosensor, derived from fangchinoline and o-phenylenediamine, was successfully prepared by hydrothermal way. The prepared carbon dots with three colors were purified with dialysis, thin layer chromatography and chromatographic column. Highly green fluorescence of Fan,N-CDs was quenched by new coccine with inner filter effect. The dependence of the ratiometric fluorescent response on new coccine concentrations was found linear over the range of 0–12.5 μM and 20–55 μM with LOD of 30.12 nM and 54.85 nm, respectively. The linearity of UV absorption ranged from 0 to 45 μM with of LOD 1.98 nM. In addition, the nanosensor was used to determine new coccine in energy drinks, carbonated beverage, gum and ketchup. It provides a new insight on the detection of new coccine by the dual-mode nanosensor.

A novel intelligently integrated MOF-based ratio fluorescence sensor for ultra-sensitive monitoring of TC in water and food samples

In this work, a high-precision visual and point-of-care testing (POCT) ratiometric fluorescent nanosensor for TC was constructed by embedding fluorescein (FL) into l-histidine modified ZIF-8 (LZIF-8) and chelating with rare earth citrate complex. Upon exposure to TC, the coordination and energy transfer between Eu3+ and TC make Eu3+ sensitized emission characteristic red fluorescence, while without prejudice to the emission peak intensity of FL. This ratiometric fluorescent probe with stable reference signal had the characteristics of high sensitivity (ultralow LOD = 5.99 nM) and selectivity and fast response kinetics (within 20 s). The high-bright fluorescence emission was beneficial to human eye recognition and it can realize semi-quantitative detection of TC in eggs, meeting the requirements of household use. In addition, the color can be read and analyzed quickly with the help of smart phone color analysis APP, and the semi-quantitative concentration of TC can be determined more conveniently.

Ratiometric fluorescence biosensor for imaging of protein phosphorylation levels in atherosclerosis mice

Atherosclerosis (AS) is the main cause of coronary heart disease, cerebral infarction and peripheral vascular disease, which is an important disease threatening human health. Abnormal levels of protein phosphorylation are closely related to the occurrence and development of diseases. Herein, the ratiometric fluorescence nanosensor (PCN/W– B@BSA) was prepared by using metal-organic frameworks (PCN-224) and fluorescent nanocluster wool-balls, which was applied for ratiometric fluorescence imaging of protein phosphorylation level in the AS mice model. Specific recognition of phosphorylation sites was achieved via specific interaction between active center Zr(IV) and phosphate. Using the two-photon property of porphyrin, the background is significantly reduced, and the sensitivity of imaging analysis is improved by combining with ratio imaging. Bovine serum albumin (BSA) was used to modify the surface of the nanosensor to reduce the non-specific adsorption and improve the biocompatibility of the nanosensor. Finally, the fluorescence nanosensor was successfully apply to fluorescence imaging of protein phosphorylation level in AS mice model, and the results showed that the protein phosphorylation level in the AS mice model was lower than that of the normal mice. The present study provides suitable fluorescence tool for further revealing phosphorylation related signaling pathways and disease mechanisms.

IFE based nanosensor composed of UCNPs and Fe(II)-phenanthroline for detection of hypochlorous acid and periodic acid

Oxidizing ClO− and IO4− exist widely in environment and are closely related to the health of organisms. Accordingly, fast, sensitive, and direct detection of the two species is significant. Using IFE in UCNPs @PAA and Fe(II)-phenanthroline system, an elegant ratiometric fluorescent nanosensor, without noble metal nanoparticle, was designed for the detection of ClO− and IO4−. Fe(II)-phenanthroline complex is used as fluorescent absorber, which can quench green light of UCNPs with gradually varied extent depending on the concentration of Fe(II). The linear zone extends to 800 and 120 μmol/L while the detection limit is 1.30 and 0.58 μmol/L for NaClO and NaIO4, respectively. Finally, the nanosensor was successfully applied to detect NaClO and NaIO4 spiked in milk, spring water, and tap water with good recoveries.

Dual-emissive ratiometric fluorescent nanosensor based on multi-nanomaterials for Ag+ determination in lake water

In this study, a sensitive ratiometric fluorescent nanosensor was constructed using a facile one-pot method by encapsulating carbon dots (CDs) and cadmium telluride quantum dots (CdTe QDs) into the pore cavities of a metal-organic framework (ZIF-8). In this nanosensor (CD/CdTe QD@ZIF-8), the fluorescence attributed to CdTe QDs was quenched by silver ions (Ag+), and the fluorescence intensity of CDs did not change. The introduction of ZIF-8 into the system can not only adsorb Ag+ but also easily separate CDs and CdTe QDs from the matrix. The developed CD/CdTe QD@ZIF-8 composite used as a ratiometric fluorescent probe exhibited high sensitivity and selectivity towards Ag+. The working linear range was 0.1-20 μM with a limit of detection (LOD) of 1.49 nM. Finally, the proposed nanosensor was applied to determine Ag+ in lake water with satisfactory results.