Ratiometric Nanosensor Research Articles

Near infrared-response ratiometric fluorescence sensor for the sensitive detection of Cu2+

The design of novel Cu2+ quantitative sensors with highly sensitivity and selectivity is a hot topic of modern chemistry. Herein, a novel ratiometric fluorescence (PL) sensor based on the red-emitting CdTeS quantum dots (QDs) and blue-emitting polyethyleneimine-functionalized carbon dots (PEI-CDs) was firstly designed for sensing Cu2+. In the presence of Cu2+, a good linear relationship between the ratios (F520/F690) of the two peak intensities and the concentrations of Cu2+ was observed in the range of 0.01–250 µM with the correlation coefficient (R2) of 0.993 and the detection limit as low as 8.07 nM. The ratiometric nanosensor was also used to successfully determine Cu2+ in plasma samples with satisfactory results obtained. Therefore, we hold the opinion that the developed ratiometric fluorescent sensor based on CdTeS QDs/PEI-CDs will provide technical support for the point-of-caretesting of Cu2+.

Dual-signaling amplification strategy for glutathione sensing by using single gold nanoelectrodes

A new nanosensor for glutathione (GSH) detection by use of single nanoelectrodes has been developed through a dual-signaling ratiometric amplification strategy. Ag nanoparticles (Ag NPs) metalized DNA1 was modified on an Au nanoelectrode surface. Due to the strong affinity between Ag NP and GSH, Ag NPs could be removed by the addition of GSH. The remaining metalized DNA1 could hardly form a double strand, while the de-metalized DNA1 could hybrid with DNA2 and DNA3 to form a complex structure to adsorb methylene blue (MB), and then the electrochemical signal of differential pulse voltammetry (DPV) from MB oxidation could be observed. With the addition of GSH, the peak current of MB oxidation at about −0.27 V (IMB) increases, while the signal of Ag oxidation at about 0.1 V (IAg) decreases. It was found that there had a linear relationship between the ratio of dual-signal (IMB/IAg) and the GSH concentrations, which could be used to detect GSH. The ratiometric nanosensor is label-free, easy to operate, and can eliminate inherent system errors. Considering the advantages of nanoelectrodes, such as low IR drop, fast response, and small overall dimension, this developed nanosensor can be used for GSH detection living systems (e.g., cell lysate).

Phagosomal pH Regulation: Revealing the Phagosomal pH Regulation and Inflammation of Macrophages after Endocytosing Polyurethane Nanoparticles by A Ratiometric pH Nanosensor (Adv. Biology 1/2021)

Phagosomal pH Regulation: Revealing the Phagosomal pH Regulation and Inflammation of Macrophages after Endocytosing Polyurethane Nanoparticles by A Ratiometric pH Nanosensor (Adv. Biology 1/2021)

Revealing the Phagosomal pH Regulation and Inflammation of Macrophages after Endocytosing Polyurethane Nanoparticles by A Ratiometric pH Nanosensor.

The effect of the intracellular pH of macrophages after taking up biodegradable polymer nanoparticles (NPs) on immunomodulating functions has not been explored so far. Previous studies have demonstrated that biodegradable polyurethane (PU) NPs exhibit immunosuppressive activity. Yet, the intracellular mechanism is not clearly understood. In this study, a uniquely designed pH nanosensor is employed for tracking the intracellular pH value of macrophages to reveal the intracellular journey of PU NPs and to clarify the intracellular pH effect on the corresponding inflammatory response. First, fluorescent mesoporous silica nanoparticles (FRMSNs) is used to detect the pH change in macrophages after endo/phagocytosis of PU NPs. Second, PU is coated on the external surface of FRMSNs to examine the intracellular trafficking process of PU in the macrophages. The results show that the majority of PU-coated FRMSNs remain to stay at the cytosol-early endosome/phagosome regions. The intracellular pH value and other supporting results show that the immune response of PU NPs may be correlated to their internalization journey. The retardation in the degradation process of the PU NPs may intervene with the lysosome activity and repress the immunostimulatory effect, which contributes to the low immune response of PU NPs.

A Mimosa-Inspired Cell-Surface-Anchored Ratiometric DNA Nanosensor for High-Resolution and Sensitive Response of Target Tumor Extracellular pH

Mimosa, a peculiar plant, can close immediately in response to external stimuli. Inspired by the stimuli-responsive behavior of mimosa, we designed a Y-shaped DNA nanosensor (regarded as DNA nanomimosa, DNM) for target tumor extracellular pH (pHe) sensing. The DNM consisted of four single-strand DNA strands, where A-strand contained an aptamer fragment and labeled with Cy5 at the 5'-end, I-strand contained an i-motif fragment, and the 3'-ends of L-strand and B-strand were labeled with Rox and BHQ2, respectively. Initially, the DNM was in an "open" state, Cy5 was separated from Rox and performed fluorescence resonance energy transfer (FRET) with neighboring BHQ2, and only Rox emitted fluorescence. When the DNM was anchored onto the cell surface through the aptamer fragment, the i-motif fragment tended to form a quadruple-helix structure due to low pH stimuli, releasing B-strand and bringing the DNM into a "close" state like stimulated mimosa. At this time, Cy5 was separated from BHQ2 but close to Rox, which led to the FRET signal generation between Rox and Cy5. The FRET ratio (Cy5/Rox) could be used as a signal for pHe sensing. Using the aptamer as an anchoring element, the DNM exhibited high cell-membrane-anchoring efficiency and excellent specificity. Additionally, relying on the pH-sensitive i-motif and twice FRET signaling mechanism, the DNM possessed a narrow pH response range (0.50 units) and performed imaging of pHe with high resolution. With these advantages, the DNM is expected to be a useful tool for the investigation of the tumor extracellular pH-related physiological processes.

Integrating peroxidase-mimicking activity with photoluminescence into one framework structure for high-performance ratiometric fluorescent pesticide sensing

We develop a robust ratiometric fluorescent nanosensor based on bifunctional Fe-based metal–organic frameworks (NH2-MIL-101(Fe)) for high-performance pesticide determination. The NH2-MIL-101(Fe) plays dual roles: the 2-aminoterephthalic acid ligand endows the framework with a photoluminescence at 428 nm, and the Fe node exhibits peroxidase-mimetic catalytic activity to oxidize the o-phenylenediamine substrate to diaminophenazine (DAP) with a fluorescence at 556 nm, which in turn suppresses the intrinsic signal (428 nm) of NH2-MIL-101(Fe) due to inner filter effect. When acetylcholinesterase is introduced for hydrolyzing acetylthiocholine chloride to thiocholine, the product with certain reducibility can inhibit the o-phenylenediamine oxidation, resulting in the DAP signal suppression (556 nm) and the NH2-MIL-101(Fe) one recovery (428 nm). Since pesticide residues effectively inhibit the activity of acetylcholinesterase, their presence can increase the formation of DAP and its fluorescence at 556 nm, thus the inherent signal of NH2-MIL-101(Fe) at 428 nm is suppressed again. By taking carbaryl as a pesticide model, the ratiometric nanosensor exhibits good sensitivity for carbaryl sensing in the scope of 2–100 ng/mL with a 1.45 ng/mL detection limit. No notable interferences from other species are observed for target detection. Moreover, our nanosensor is confirmed to be reliable for carbaryl analysis in real samples.

Real-time monitoring of glutathione in living cells using genetically encoded FRET-based ratiometric nanosensor

Reduced glutathione (GSH) level inside the cell is a critical determinant for cell viability. The level of GSH varies across the cells, tissues and environmental conditions. However, our current understanding of physiological and pathological GSH changes at high spatial and temporal resolution is limited due to non-availability of practicable GSH-detection methods. In order to measure GSH at real-time, a ratiometric genetically encoded nanosensor was developed using fluorescent proteins and fluorescence resonance energy transfer (FRET) approach. The construction of the sensor involved the introduction of GSH binding protein (YliB) as a sensory domain between cyan fluorescent protein (CFP; FRET donor) and yellow fluorescent protein (YFP; FRET acceptor). The developed sensor, named as FLIP-G (Fluorescence Indicator Protein for Glutathione) was able to measure the GSH level under in vitro and in vivo conditions. When the purified FLIP-G was titrated with different concentrations of GSH, the FRET ratio increased with increase in GSH-concentration. The sensor was found to be specific for GSH and also stable to changes in pH. Moreover, in live bacterial cells, the constructed sensor enabled the real-time quantification of cytosolic GSH that is controlled by the oxidative stress level. When expressed in yeast cells, FRET ratio increased with the external supply of GSH to living cells. Therefore, as a valuable tool, the developed FLIP-G can monitor GSH level in living cells and also help in gaining new insights into GSH metabolism.

Fluorescent nanosensor designing via hybrid of carbon dots and post-imprinted polymers for the detection of ovalbumin

We reported a facile strategy to assemble a ratiometric nanosensor for the ovalbumin (OVA) fluorescence determination and meanwhile it can be utilized for selective visual identification by naked eyes with fluorescent test papers under 365 nm UV lamp. The nanosensor was prepared through simply mixing blue color carbon dots (CDs) and green color core-shell imprinted polymers. Blue CDs were used directly as the internal reference without participating in the imprinting process and modified molecularly imprinted polymers (MIPs) were synthesized by post-imprinting, using fluorescein isothiocyanate (FITC) as fluorescence enhanced signal. Upon the addition of different concentrations of OVA, the fluorescence intensity of FITC was enhanced, while the fluorescence intensity of CDs was almost unchanged, leading to a detection limit as low as 15.4 nM. Accordingly, the fluorescence color was gradually changed from blue to dark olive green to green with naked eyes observation. Moreover, the ratiometric nanosensor was successfully applied to detect OVA in the human urine samples with satisfactory recoveries attaining of 92.0–104.0% with relative standard deviation (RSD) of 3.3–3.9% and 93.3–101.0% with RSDs of 2.7–3.8% for the spiked chicken egg white samples. This strategy reported here opens a novel pathway for biomacromolecule detection in real applications and can realize the visual observation on fluorescent test papers.

Development and application of a ratiometric nanosensor for measuring pH inside the gastrointestinal tract of zooplankton

The pH in the anterior gut of Daphnia magna is more than 2 pH units lower than the cultural medium.

Two-Photon Excitation/Red Emission, Ratiometric Fluorescent Nanoprobe for Intracellular pH Imaging.

Herein, we describe a novel two-photon excitation/red emission-based ratiometric pH nanosensor consisting of a pH-sensitive two-photon dye and Tm3+-doped upconversion nanoparticles (UCNP). The fluorescence emission ratio between the dye (610 nm) and UCNPs (810 nm) (I610/I810) provides a linear indicator of pH values in the range from pH 4.0 to 6.5 with high sensitivity. These nanoprobes selectively accumulate in the lysosomes of cells, making them suitable for lysosomal pH tracking. This pH nanoprobe has been successfully applied in visualizing chemically stimulated changes of intracellular pH in living cells and tissues.

Dual-Emissive Metal-Organic Framework as a Fluorescent "Switch" for Ratiometric Sensing of Hypochlorite and Ascorbic Acid.

The detection of hypochlorite (ClO-) content in tap water is extremely important because excess amounts of hypochlorite can convert into highly toxic species and inadequate amounts of hypochlorite cannot fully kill bacteria and viruses. Although several metal-organic frameworks (MOFs) have been successfully employed as fluorescent sensors for hypochlorite detection, all these sensors are based on single emission that responds to the dose of hypochlorite. Ratiometric sensors are highly desirable, which can improve the sensitivity, accuracy, and reliability via self-calibration. Herein, a nanoscale dual-emission multivariate 5-5-Eu/BPyDC@MOF-253-NH2 was synthesized by sequential mixed-ligand self-assembly and postsynthesis method. Among the two emission bands of 5-5-Eu/BPyDC@MOF-253-NH2, the strong blue emitting derived from ligands is sensitive to hypochlorite, while the red emitting derived from Eu(III) almost keeps invariable. Therefore, 5-5-Eu/BPyDC@MOF-253-NH2 was exploited as a fluorescent ratiometric nanosensor for "on-off" sensing of hypochlorite. Notably, the proposed sensing system showed an excellent performance including fast response (within 15 s), relative high specificity, wide linear range (0.1-30 μM), and low detection limit (0.094 μM). Besides, the suppressed blue emitting was recovered after the addition of ascorbic acid (AA) that consumes ClO- via the redox reaction. Therefore, 5-5-Eu/BPyDC@MOF-253-NH2 was further employed as a fluorescent ratiometric nanosensor for the "on-off-on" sensing of AA. This work represents the first MOF-based fluorescent "switch" for the ratiometric sensing of hypochlorite and the second for ratiometric sensing of AA.

A new dual-recognition strategy for hybrid ratiometric and ratiometric sensing perfluorooctane sulfonic acid based on high fluorescent carbon dots with ethidium bromide.

In this work, a novel strategy for perfluorooctane sulfonic acid (PFOS) detection was established by using a ratiometric nanosensor with the combination of fluorescence and second-order scattering (SOS). The practical ratiometric nanosensor was synthesized simply by mixing fluorescent dye ethidium bromide (EB) and nitrogen doped carbon dots (N-CDs) which was synthesized by a one-step hydrothermal method with Victoria Blue B, possessing three emission peaks at 472 nm, 560 nm and 600 nm under a single wavelength excitation of 280 nm, respectively. The EB served as the reference signal label, and the N-CDs, having response to the analytes, acted as the response signal label. To achieve ratiometric detection, the fluorescence emission of the N-CDs was turned off and the SOS emission was turned on with the addition of the target PFOS. To achieve colorimetric detection, with the help of EB, the fluorescence of the system changed from green to orange. Under the optimal conditions, the difference of F472/I568 of the nanosensor had good linearity against the concentrations of PFOS within a linear range of 0-2.0 μM. The limit of detection was as low as 27.8 nM, which was low enough for the detection of PFOS in water samples. The proposed method has been successfully applied to the detection of PFOS with RSD <1.67%. The results show that the as-prepared N-CDs/EB ratiometric nanosensor has potential application for the detection of PFOS in environmental monitoring.

Fluorescence-Based Ratiometric Nanosensor for Selective Imaging of Cancer Cells

Herein, we report the synthesis and characterization of a nanosensor developed from a group of uniform materials based on organic salts (GUMBOS). This sensor is composed of three ionic species, nam...

A two-target responsive reversible ratiometric pH nanoprobe: a white light emitting quantum dot complex.

Herein we report the use of a white light emitting quantum dot complex (comprising an orange emitting Mn2+-doped ZnS quantum dot and greenish-blue emitting zinc-quinolate complex) as a two-target responsive ratiometric reversible pH nanosensor in the physiological range of 6.5-10.3, following changes in their luminescence intensity ratio, color and chromaticity.

Self-Assembly of a Monochromophore-Based Polymer Enables Unprecedented Ratiometric Tracing of Hypoxia.

The accuracy of traditional bischromophore-based ratiometric probes is always compromised by undesirable energy/charge transferring interactions between the internal reference moiety and the sensing chromophore. In this regard, ratiometric sensing with a monochromophore system is highly desirable. Herein, an unprecedented monochromophore-based ratiometric probe, which consists of a hydrophilic backbone poly(N-vinylpyrrolidone) (PVP) and single chromophore of platinum(II) tetraphenylporphyrin (Pt-TPP) is reported. Combination of the specific assembled clustering-triggered fluorescent emission (oxygen-insensitive) with the original Pt-TPP phosphorescence (oxygen-sensitive) enables successful construction of a monochromophore-based ratiometric nanosensor for directly tracing hypoxia in vivo, along with the preferable facilitation of enhanced permeation and retention effect and long excitation wavelength. The unique ratiometric signals enable the direct observation from normoxic to hypoxic environment in both living A549 cells and a tumor-bearing mice model, providing a significant paradigm of a monochromophore-based dual-emissive system with the specific assembled cluster emission. The work satisfactorily demonstrates a valuable strategy for designing monochromophore-based dual-emissive materials, and validates its utility for in vivo ratiometric biological sensing without the common energy/charge interference in bischromophore-based system.

A single fluorophore ratiometric nanosensor based on dual-emission DNA-templated silver nanoclusters for ultrasensitive and selective Pb2+ detection

Lead ion (Pb2+) is known as a major non-degradable environmental pollutant and is quite harmful to human health. In our investigation, a novel ratiometric fluorescent nanosensor with DNA-AgNCs as single fluorophore has been successfully constructed for ultrasensitive and specific detection of Pb2+. The single-strand DNA templated silver nanoclusters present green emission, which can be converted into red emission after approaching a specific DNA segment by forming duplex with its complementary DNA strands (ds-DNA-AgNCs). The ds-DNA-AgNCs contains rA cleavage site of Pb2+-dependent DNAzyme configuration. In the presence of Pb2+, the specific DNA segment would be released from the ds-DNA-AgNCs, resulting in discoloration of DNA-AgNCs from red to green. Since Pb2+ can successively cleave the rA site, the signal change from red to green emission is amplified. Thus, benefiting from the Pb2+-dependent DNAzyme and the charming properties of DNA-AgNCs, the proposed platform exhibits a good linear relationship from 0.001 nM to 10 nM with a detection limit of 1.0 pM for Pb2+ determination, which is lower than most of the reported Pb2+ biosensors. Moreover, this sensitive ratiometric fluorescent probe exhibits excellent selectivity toward Pb2+ detection in real samples, such as lake water, tap water, and human serum samples, illustrating the huge potential applications for complicated samples in the future.

Dual-Emission Fluorescent Microspheres for the Detection of Biothiols and Hg2.

Dual-emission nanosensor for Hg2+ detection was prepared by coupling CA-AEAPMS on the surface of RBS-doped modified silica microspheres. The CA-AEAPMS was synthesized by using N-(β-aminoethyl)-γ-aminopropyl methyldimethoxysilane (AEAPMS) and citric acid as the main raw material. The obtained nanosensor showed characteristic fluorescence emissions of Rhodamine B (red) and CA-AEAPMS (blue) under a single excitation wavelength (360 nm). Upon binding to Hg2+, only the fluorescence of CA-AEAPMS was quenched, resulting in the ratiometric fluorescence response of the dual-emission silica microspheres. This ratiometric nanosensor exhibited good selectivity to Hg2+ over other metal ions, because of the amide groups on the surface of CA-AEAPMS serving as the Hg2+ recognition sites. The ratio of F450/F580 linearly decreased with the increasing of Hg2+ concentration in the range of 0 to 3 × 10−6 M, and a detection limit was as low as 97 nM was achieved. Then, the addition of three thiol-containing amino acids (Cys, Hcy, GSH) to the quenched fluorescence solution with Hg2+ can restore the fluorescence, and the detection limits of the three biothiols (Cys, Hcy, GSH) are 0.133 μM, 0.086 μM, and 0.123 μM, respectively.

Benzoperylene probe/ZnS quantum dots nanocomposite for the ratiometric detection and intracellular imaging of highly reactive oxygen species

A ratiometric nanosensor for the selective detection and intracellular imaging of highly reactive oxygen species (hROS) is developed. Benzoperylene probe and Mn-ZnS quantum dots based nanoparticles were fabricated through cost effective and simple procedures. The nanoparticles exhibit distinct excimer emission and long-lived room-temperature phosphorescence (RTP) emission at the same time under single wavelength excitation. The nanosensor shows highly sensitive and selective ratiometric response towards hROS over other ROS. The dual emission property also endows the nanoparticles the capability for sensitive live cell imaging of hROS, and the potential for real time monitoring of intracellular hROS.

DNA Origami-Based Förster Resonance Energy-Transfer Nanoarrays and Their Application as Ratiometric Sensors.

DNA origami nanostructures provide a platform where dye molecules can be arranged with nanoscale accuracy allowing to assemble multiple fluorophores without dye-dye aggregation. Aiming to develop a bright and sensitive ratiometric sensor system, we systematically studied the optical properties of nanoarrays of dyes built on DNA origami platforms using a DNA template that provides a high versatility of label choice at minimum cost. The dyes are arranged at distances, at which they efficiently interact by Förster resonance energy transfer (FRET). To optimize array brightness, the FRET efficiencies between the donor fluorescein (FAM) and the acceptor cyanine 3 were determined for different sizes of the array and for different arrangements of the dye molecules within the array. By utilizing nanoarrays providing optimum FRET efficiency and brightness, we subsequently designed a ratiometric pH nanosensor using coumarin 343 as a pH-inert FRET donor and FAM as a pH-responsive acceptor. Our results indicate that the sensitivity of a ratiometric sensor can be improved simply by arranging the dyes into a well-defined array. The dyes used here can be easily replaced by other analyte-responsive dyes, demonstrating the huge potential of DNA nanotechnology for light harvesting, signal enhancement, and sensing schemes in life sciences.

“On-off-on” fluorescent system for detection of Zn2+ in biological samples using quantum dots-carbon dots ratiometric nanosensor

In this work, a novel strategy for Zn2+ detection was established by using an “on-off-on” ratiometric fluorescent nanosensor with the help of ethylene diaminetetraacetic acid (EDTA), a common metal chelating agent. The simple and practical ratiometric fluorescent nanosensor was synthesized by covalently binding CdTe quantum dots (QDs) and carbon dots (CDs), possessing two emission peaks at 525 nm and 450 nm under a single wavelength excitation of 360 nm, respectively. The CdTe QDs served as the response signal label, and the CDs, having no response to the analytes, acted as the reference signal. The fluorescence emission of the nanosensor was turned off to create a low-level “off” state when EDTA was added, and turned on dramatically with the addition of the target Zn2+. Under the optimal conditions, the change of the fluorescence intensity ratio of the nanosensor at 525 nm and 450 nm (ΔF525/F450) had good linearity against the concentrations of Zn2+ within a dynamic linear range of 0.50–40 μM. The limit of detection was as low as 0.33 μM (3σ/K), which was low enough for the detection of Zn2+ in human body. The proposed method was successfully applied to the detection of Zn2+ in human urine and plasma with RSDs less than 10%. The results show that the as-prepared QDs-CDs ratiometric nanosensor has potential application of clinical detection of Zn2+ in the human body.