Change Of Fluorescence Intensity Ratio Research Articles

Visual colorimetric label for real-time monitoring of SO2 concentration change in grape and mango during storage

Sulfur dioxide (SO2) is widely utilized as a preservative in food transportation and storage, but excessive consumption poses health risks. This study presents a novel and efficient method for the real-time detection of SO2 using a sensor named TK, synthesized from triphenylamine and 2-cyanomethyl-1-methyl-quinolinium. The core mechanism involves the Michael addition reaction of the CC bond in TK with SO2, which disrupts the intramolecular charge transfer process, resulting in a significant color change and a blue shift in fluorescence emission. Methodologically, the sensor's response was quantified by the change in fluorescence intensity ratio (I425/I647) within a SO2 concentration range of 0–180 μM. The sensor exhibited high sensitivity and selectivity. For practical application, TK was incorporated into hydrophilic polyvinyl alcohol to create a smart label capable of visual colorimetry and fluorescence analysis. SO2 concentration changes were monitored by using this label, demonstrated by the color transition from burgundy red to colorless, yielding a maximum color difference (ΔE) of 73.6. The smart label was successfully used to monitor the quality of various grapes and mangoes during long-term storage, providing a reliable, equipment-independent method suitable for household use. The study offers a new tool for enhancing food safety and mitigating health risks associated with SO2 exposure.

Optical temperature sensing of four modes by using CsPb(Cl/Br)3 quantum dots and Tb3+ ions co-doping glass

We have fabricated CsPb(Cl/Br)3 quantum dots (QDs) and Tb3+ co-doping glass and comparatively investigated four-mode temperature sensing of fluorescence intensity ratio (FIR), full width at half maximum (FWHM), lifetime and chromatic coordinate. Temperature dependent photoluminescence (PL) spectra are measured. The Tb3+ ions and CsPb(Cl/Br)3 QDs have independent luminescence and FIR of Tb3+ to QDs has obvious decrease with temperature, which is used for FIR temperature sensing. The PL and PL decay of QDs are used for FWHM and lifetime temperature sensing. The change of FIR with temperature leads to the change of luminous color and chromatic coordinate with temperature. A new chromatic temperature sensing method is established, which utilizes linear relation of chromatic coordinate and temperature. Temperature dependence for FIR, FWHM, lifetime and chromatic coordinate has been fitted. Absolute sensitivity, relative sensitivity, temperature accuracy and repeatability have been evaluated. Among the four sensing modes, the FIR and chromatic coordinate modes have large sensitivity and small accuracy. The FIR mode is better than chromatic coordinate mode in absolute sensitivity and relative sensitivity, whereas the chromatic coordinate mode is better in its good linear relation. The four sensing modes have excellent repeatability due to the stability of QDs-Tb3+ co-doping glass.

Ratiometric fluorescence immunoassay of SARS-CoV-2 nucleocapsid protein via Si-FITC nanoprobe-based inner filter effect.

The global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus has necessitated rapid, easy-to-use, and accurate diagnostic methods to monitor the virus infection. Herein, a ratiometric fluorescence enzyme-linked immunosorbent assay (ELISA) was developed using Si-fluorescein isothiocyanate nanoparticles (FITC NPs) for detecting SARS-CoV-2 nucleocapsid (N) protein. Si-FITC NPs were prepared by a one-pot hydrothermal method using 3-aminopropyl triethoxysilane (APTES)-FITC as the Si source. This method did not need post-modification and avoided the reduction in quantum yield and stability. The p-nitrophenyl (pNP) produced by the alkaline phosphatase (ALP)-mediated hydrolysis of p-nitrophenyl phosphate (pNPP) could quench Si fluorescence in Si-FITC NPs via the inner filter effect. In ELISA, an immunocomplex was formed by the recognition of capture antibody/N protein/reporter antibody. ALP-linked secondary antibody bound to the reporter antibody and induced pNPP hydrolysis to specifically quench Si fluorescence in Si-FITC NPs. The change in fluorescence intensity ratio could be used for detecting N protein, with a wide linearity range (0.01–10.0 and 50–300 ng/mL) and low detection limit (0.002 ng/mL). The concentration of spiked SARS-CoV-2 N protein could be determined accurately in human serum. Moreover, this proposed method can accurately distinguish coronavirus disease 2019 (COVID-19) and non-COVID-19 patient samples. Therefore, this simple, sensitive, and accurate method can be applied for the early diagnosis of SARS-CoV-2 virus infection.Electronic Supplementary MaterialSupplementary material (characterization of Si-FITC NPs (FTIR spectrum, XRD spectra, and synchronous fluorescence spectra); condition optimization of ALP response (fluorescence intensity ratio change); mechanism investigation of ALP response (fluorescence lifetime decay curves and UV—vis absorption spectra); detection of N protein using commercial ELISA Kit; analytical performance of assays for ALP detection or SARS-CoV-2 N protein detection; and determination results of SARS-CoV-2 N protein in human serum) is available in the online version of this article at 10.1007/s12274-022-4740-5.

Exploring the Impact of Structure-Sensitivity Factors on Thermographic Properties of Dy3+-Doped Oxide Crystals.

Optical absorption spectra and luminescence spectra were recorded as a function of temperature between 295 K and 800 K for single crystal samples of Gd2SiO5:Dy3+, Lu2SiO5:Dy3+, LiNbO3:Dy3+, and Gd3Ga3Al2O12:Dy3+ fabricated by the Czochralski method and of YAl3(BO3)4:Dy3+ fabricated by the top-seeded high temperature solution method. A thermally induced change of fluorescence intensity ratio (FIR) between the 4I15/2→ 6H15/2 and 4F9/2 → 6H15/2 emission bands of Dy3+ was inferred from experimental data. It was found that relative thermal sensitivities SR at 350 K are higher for YAl3(BO3)4:Dy3+ and Lu2SiO5:Dy3+than those for the remaining systems studied. Based on detailed examination of the structural peculiarities of the crystals it was ascertained that the observed difference between thermosensitive features cannot be attributed directly to the dissimilarity of structural factors consisting of the geometry and symmetry of Dy3+ sites, the number of non-equivalent Dy3+ sites, and the host anisotropy. Instead, it was found that a meaningful correlation between relative thermal sensitivity SR and rates of radiative transitions of Dy3+ inferred from the Judd–Ofelt treatment exists. It was concluded that generalization based on the Judd–Ofelt parameters and luminescence branching ratio analysis may be useful during a preliminary assessment of thermosensitive properties of new phosphor materials.

Highly sensitive label-free fluorescence determination of lymphotropic virus DNA based on exonuclease assisted target recycling amplification and in-situ generation of fluorescent copper nanoclusters

Specific and sensitive detection of target DNA plays a significant role in clinical diagnosis and biomedical research. Herein, a sensitive ratio fluorescence biosensor was constructed based on in-situ generation of fluorescent copper nanoclusters (CuNCs) on the DNA modified graphene quantum dots (GQDs) for the detection of HTLV-I DNA. Firstly, large amount of AT rich single DNA (o-DNA) can be released from the designed hairpin DNA in the presence of trace target DNA via exonuclease III assisted target recycling amplification strategy. Then, the released o-DNA hybridized with the complementary DNA1 which was modified on the surface of GQDs, and the formed hybridized DNA with blunt 3′-hydroxylated terminus that couldn’t be digested by exonuclease I could act as the template for the generation of fluorescent CuNCs. While in the absence of target DNA, the o-DNA couldn’t be released, thus the DNA1 with 3′overhang ends could be degraded by exonuclease I, which resulted in the in-situ generation of fluorescent CuNCs on the surface of GQDs was blocked owing to the lack of DNA template. The GQD fluorescence in the GQD-CuNC nanohybrid was almost uninfluenced during the whole process. Therefore, with the GQD serving as the reference and CuNC acting as the reporter signal, there was an excellent linear relationship between the change of fluorescence intensity ratio (F595/F445) and the concentration of HTLV-I DNA in the range of 20 pM-12 nM with a detection limit of 10 pM. Furthermore, the biosensor exhibited satisfactory results for monitoring the presence of HTLV-I DNA in human serum.

Europium-functionalized luminescent titania nanotube arrays: Utilizing interactions with glucose, cholesterol and triglycerides for rapid detection application

In this work, titania nanotube arrays (TiO2-NTs) were prepared by anodization, and the Eu(III) complexes (Eu (TTA)3 phen with 2-thenoyltrifluoroacetone (TTA) and 1, 10-phenanthroline (phen)) were successfully coated onto the walls of the nanotubes. When a solution of glucose, cholesterol or triglycerides was dropped onto Eu(III) complex-modified TiO2-NTs, the fluorescence intensity of this material changes (glucose enhances fluorescence, cholesterol and triglycerides quench fluorescence). These phenomena are explained via an energy transfer process. The sensitivity of the fluorescence intensity to glucose, cholesterol or triglycerides concentration enables design of a multifunctional solid sheet-like detector. Under optimized experimental conditions, the change in fluorescence intensity ratio (ΔF/F0) is linear with the concentration of glucose, cholesterol or triglycerides. To test the utility of the detector, glucose in orange juice, cholesterol in milk powder, and triglycerides in coconut oil were measured using this method and the results were in good agreement analytical data provided by a food testing company. The new method proposed here is simple, sensitive, reliable and suitable for practical applications.

Copper nanoclusters @ nitrogen-doped carbon quantum dots-based ratiometric fluorescence probe for lead (II) ions detection in porphyra

A novel ratiometric fluorescence probe was proposed for detecting lead (II) ions (Pb2+) in porphyra, the approach was based on copper nanoclusters and nitrogen-doped carbon quantum dots (CuNCs-CNQDs). In this probe, the CuNCs delivered the response signal, the fluorescence of which was enhanced by Pb2+ due to the aggregation-induced emission enhancement (AIEE) between Pb2+ and CuNCs. The CNQDs provided the self-calibration signal, whose fluorescence remained almost unchanged in coexistence with Pb2+. According to the change of fluorescence intensity ratio between the fluorophores, CuNCs–CNQDs nanohybrid was used as ratiometric probes for the sensitive detection of Pb2+ in the range of 0.010–2.5 mg L−1, with a detection limit of 0.0031 mg L−1. Finally, the probe was successfully applied to detect Pb2+ in porphyra with relative standard deviations (RSDs) lower than 5%. This study provides a straightforward, stable, and sensitive approach for detecting Pb2+ in porphyra.

Effect of temperature on up-conversion phenomena in Gd3(Al,Ga)5O12 crystals co-doped with Yb3+ and Tm3+

Single crystals of Gd3(Al,Ga)5O12 with intentional stoichiometry Gd3Ga2.5Al2.5O12 doped with 1%Tm3++x%Yb3+; (x = 1, 3, 5); were grown by the Czochralski method. Spectra and intensities of up-converted luminescence excited at 975 nm or 803 nm were measured as a function of temperature within 295 K–775 K region. It was found that for the two excitation wavelengths the growth of temperature brings about a decrease of an up-converted blue luminescence intensity. Thermally enhanced growth of nonradiative relaxation rates for excited states involved in the up-conversion process was determined based on an analysis of respective luminescence decay curves. Temperature-dependent change of fluorescence intensity ratio (FIR) for the 3F3,2 – 3H6/3H4 – 3H6 up-converted bands was observed and resulting absolute temperature sensitivity of 0.058 K-1 was found for GAGG:1%Tm,3%Yb at 725 K.

Temperature-dependent persistent luminescence of SrAl2O4:Eu2+, Dy3+, Tb3+: a strategy of optical thermometry avoiding real-time excitation.

A new strategy of optical thermometry is realized by long persistent luminescence phosphor SrAl2O4:Eu2+, Dy3+, Tb3+ (SAEDT). Under different temperatures, SAEDT shows bright afterglow emissions after cessation of the UV excitation. The afterglow color of the SAEDT sample is blue at 60K and gradually changed into green at 240K. The normalized afterglow spectra at different temperatures give a dramatic change of fluorescence intensity ratio between the blue band and the green band. Not only has this material exhibited a high absolute sensitivity and relative sensitivity for temperature sensing, but it also has the great advantage of eliminating the heating effect due to avoidance of real-time direct excitation.

Ratiometric fluorescent detection of copper ions using coumarin-functionalized carbon dots based on FRET

A novel FRET ratiometric fluorescent probe (CMH-GA-CDs) was designed for the detection of Cu2+ in aqueous solution. The CMH-GA-CDs were prepared through grafting 7-diethylaminocoumarin-3-carbohydrazide (HCM) on the surface of glyoxylic acid-modified carbon dots (GA-CDs) by amidation reaction. In the absence of Cu2+, a FRET pair from the CDs to CMH units was established, in which the CMH-GA-CDs exhibited dual emission bands centered at 400 nm (CDs) and 458 nm(CMH), respectively, under optimal excitation wavelength of CDs (λex = 340 nm). Upon addition of 30 μM Cu2+ to CMH-GA-CDs solution, Cu2+ coordinated with the heteroatoms N and O, which caused the inhibition of FRET process and the change of fluorescence intensity ratio I458/I400 from 1.95 to 0.91. The ratio of I458/I400 exhibited a good linear relationship with the concentration of Cu2+ in the range of 0–10 μM and the limit of detection was as low as 0.21 μM. Furthermore, The CMH-GA-CDs were used for the detection of Cu2+ in tap water and lake water with satisfactory recovery ratio between 91% and 104%, demonstrating the promising applicability for detecting Cu2+ in water samples.

The thermogenic actions of natriuretic peptide in brown adipocytes: The direct measurement of the intracellular temperature using a fluorescent thermoprobe

In addition to the various effects of natriuretic peptides (NPs) on cardiovascular systems, increasing attention is being paid to the possibility that NPs induce adipose tissue browning and activate thermogenic program. We herein established a direct intracellular temperature measurement system using a fluorescent thermoprobe and investigated the thermogenic effects of A-type NP (ANP) on brown adipocytes. The thermoprobe was successfully introduced into rat brown adipocytes, and the temperature dependent change in fluorescence intensity ratio was measured using a fluorescence microscope. After one-hour incubation with ANP, the degree of the change in fluorescence intensity ratio was significantly higher in ANP-treated (P < 0.01) adipocytes compared to untreated controls. The ANP treatment increased uncoupling protein-1 (UCP1) mRNA levels, which is one of the markers of thermogenesis in adipocytes, while the intracellular ATP content was not changed, indicating mitochondrial uncoupled respiration. Intriguingly, these thermogenic actions of ANP were more prominent when brown adipocytes were incubated at 35 °C than at 37 °C. Moreover, the increase in the intracellular temperature and the expression of UCP1 induced by ANP were cancelled by p38MAPK inhibition. Taken together, this study directly demonstrated the thermogenic actions of ANP in brown adipocytes through the use of a novel method of intracellular temperature measurement.

Quantum dots-based ratiometric fluorescence probe for mercuric ions in biological fluids

Fluorescence analysis by means of a single fluorescence signal output usually leads to the signal fluctuation caused by various external factors. Ratiometric fluorescence probes that can significantly eliminate the external effects by self-calibration of two different emission bands are preferable for the detection of real samples. In this work, we designed a dual-emission quantum dots (QDs) nanocomposite as a ratiometric probe for the visual detection of Hg(2+). The dual-emission QDs nanocomposite consists of two differently sized CdTe/CdS QDs. The red-emitting larger sized CdTe/CdS QDs embeded in silica nanoparticles are insensitive to Hg(2+), while the green-emitting smaller sized ones are covalently conjugated onto the silica nanoparticles surface and sensitive to Hg(2+). The addition of Hg(2+) can only quench green fluorescence in the dual-emission QDs nanocomposites, which triggers the change of fluorescence intensity ratio of two different emission wavelengths and hence induces the evolution of fluorescence color of the probe solution with variation of Hg(2+) concentration. Based on this feature, the dual-emission QDs nanocomposites can be used to develop a ratiometric fluorescence probe for the visual detection of Hg(2+). Under the optimized conditions, the ratiometric fluorescence QDs probe shows a linear relationship between fluorescence intensity ratio and Hg(2+) concentration in the range of 5-300 nM. The detection limit of this probe was found to be 3.1 nM. This ratiometric assay also exhibits a high selectivity and it has been successfully used in the determination of Hg(2+) content in fetal bovine serum and human urine.

A low cytotoxic and ratiometric fluorescent nanosensor based on carbon-dots for intracellular pH sensing and mapping

Intracellular pH plays a critical role in the function of cells, and its regulation is essential for most cellular processes. In this study, we demonstrate a fluorescence resonance energy transfer (FRET)-based ratiometric pH nanosensor with carbon-dot (CD) as the carrier. The sensor was prepared by covalently linking a pH-sensitive fluorescent dye (fluorescein isothiocyanate, FITC) onto carbon-dot. As the FRET donor, the carbon-dot exhibits bright fluorescence emission as well as λex-dependent photoluminescence emission, and a suitable excitation wavelength for the donor (CD) can be chosen to match the energy acceptor (fluorescein moiety). The fluorescein moieties on a CD undergo structural and spectral conversion as the pH changes, affording the nanoplatform a FRET-based pH sensor. The CD-based system exhibits a significant change in fluorescence intensity ratio between pH 4 and 8 with a pKa value of 5.69. It also displays excellent water dispersibility, good spectral reversibility, satisfactory cell permeability and low cytotoxicity. Following the living cell uptake, this nanoplatform with dual-chromatic emissions can facilitate real-time visualization of the pH evolution involved in the endocytic pathway of the nanosensor. This reversible and low cytotoxic fluorescent nanoplatform may be highly valuable in a variety of biological studies, such as endocytic trafficking, endosome/lysosome maturation, and pH regulation in subcellular organelles.

Position‐Specific Incorporation of Fluorescent Non‐natural Amino Acids into Maltose‐Binding Protein for Detection of Ligand Binding by FRET and Fluorescence Quenching

Position-specific incorporation of fluorescent groups is a useful method for analysis of the functions and structures of proteins. We have developed a method for the incorporation of visible-wavelength-fluorescent non-natural amino acids into proteins in a cell-free translation system. Using this technique, we introduced one or two BODIPY-linked amino acids into maltose-binding protein (MBP) to obtain MBP derivatives showing ligand-dependent changes in fluorescence intensity or intensity ratio. BODIPY-FL-aminophenylalanine was incorporated in place of 15 tyrosines, as well as the N-terminal Lys1, and the C-terminal Lys370 of MBP. Fluorescence measurements revealed that MBP containing a BODIPY-FL moiety in place of Tyr210 showed a 13-fold increase in fluorescence upon binding of maltose. Tryptophan-to-phenylalanine substitutions suggest that the increase in fluorescence was the result of a decrease in the quenching of BODIPY-FL by tryptophan located around the binding site. MBP containing a BODIPY-558 moiety also showed a maltose-dependent increase in fluorescence. BODIPY-FL was then additionally incorporated in place of Lys1 of the BODIPY-558-containing MBP as a response to the amber codon. Fluorescence measurements with excitation of BODIPY-FL showed a large change in fluorescence intensity ratio (0.13 to 1.25) upon binding of maltose; this change can be attributed to fluorescence resonance energy transfer (FRET) and maltose-dependent quenching of BODIPY-558. These results demonstrate the usefulness of the position-specific incorporation of fluorescent amino acids in the fluorescence-based detection of protein functions.

Change in Micro-Environments in Poly(acrylamide) Gel with Pyrenyl Probe Due to Its Volume Phase Transition Induced by pH Change

Changes in the micro-environments and interactions among the side groups during pH-induced volume phase transition of poly(acrylamide) gels having pyrenyl group as a fluorescent probe in acetone-water (9:11) mixed solvent were studied with fluorescence spectra and lifetime measurements. The results are as follows: (a) The volume phase transition is caused by hydrophobic interaction of polymer main chains and charge repulsive force of carboxylate anion at polymer side chains inside the gel, indicated by change in fluorescence intensity ratio I1/I3 of the pyrenyl probe and the shifts in fluorescence wavelength. (b) In the collapsed state, the gel consists of two phases: one is the portion of polymer main chain aggregate, and the other is the portion of polar side group assembly, which results from a competitive interaction between the hydrophobic interaction of polymer main chains and the charge repulsive force of carboxylate anion in the coexisting two phase regime.