Resonance Energy Transfer Mechanism Research Articles

Lanthanide-Based Nanoprobes for Time-Resolved Luminescence Imaging on Various Ions and Molecules

Lanthanide-doped upconversion nanoparticles (Ln-UCNPs) have been extensively explored in the biological field. In particular, Ln-UCNPs with near-infrared (NIR) fluorescence have tremendous potential for biological imaging because of their outstanding photo-and chemo-stability, extended photoluminescence lifetimes, low long-term toxicities and narrow photoluminescence bandwidths as well as minimal background interferences. Using predesigned energy transfer routes makes it possible to get upconversion luminescence from lanthanides' 4f-4f optical transitions. This article clarifies the key working principles and superiorities of Ln-UCNPs for bioimaging. A crucial overview of recent advances in biological detection adopting lanthanide-based luminescence resonance energy transfer (LRET) mechanisms is presented while emphasizing the importance of modifying Ln-UCNPs to obtain a more efficient energy transfer mechanism.

Disposable luminescent kit based on dithizone-functionalized waste blue-phosphor as field-deployable sensor for environment monitoring

A new disposable sensor based on waste blue-phosphor (BaMgAl10O17:Eu2+, BAM) embedded in polyvinyl alcohol (PVA) support and modified dithizone (Dz) was designed and fabricated for the determination of Pb2+ ions in environmental samples. Dz is used as the modifier to give indirect sensing property through interacting with BAM particles via surface coordinating reactions to form Dz-BAM conjugates resulting in quenching of natural fluorescence of BAM by fluorescence resonance energy transfer (FRET) mechanism. The Box-Behnken response surface factorial design was used to optimize the prepared sensor using two spectrophotometric and spectrofluorimetric approaches. The calibration curve was found to be linear in the range of 500–4500 nmol/L (R2 = 0.9986) with LOD of 150 nmol/L and LOQ of 500 nmol/L. The potential interference ions were studied and the applicability of the sensor was successfully evaluated by determination of the target ion in real tap and river water samples containing potential interferences.

Detection of Azo Dyes Using Carbon Dots from Olive Mill Wastes

Azo dyes are widely spread in our day life, being heavily used in cosmetics, healthcare products, textile industries, and as artificial food colorants. This intense industrial activity, which inherently includes their own production, inexorably leads to uncontrolled release of dyes into the environment. As emerging pollutants, their detection, particularly in water systems, is a priority. Herein, a fluorescence-based method was employed for the sensitive and selective detection of anionic and neutral azo dyes. Carbon dots (CDs) synthesized from wet pomace (WP), an abundant semi-solid waste of olive mills, were used as probes. An outstanding capability for detection of azo dyes methyl orange (MO) and methyl red (MR) in aqueous solutions was disclosed, which reached a limit of detection (LOD) of 151 ppb for MO. The selectivity of WP-CDs for the anionic azo dye (MO) was established through competitive experiments with other dyes, either anionic (indigo carmine) or cationic (fuchsin, methylene blue, and rhodamine 6G); perchlorate salts of transition metal cations (Cu(II), Co(II), Fe(II), Fe(III), Hg(II), and Pb(II)); and sodium salts of common anions (NO3−, CO32−, Cl−, and SO42−). Evidence has been collected that supports static quenching as the main transduction event underlying the observed quenching of the probe’s fluorescence, combined with a dynamic resonance energy transfer (RET) mechanism at high MO concentrations.

Carbon Dots Conjugated Antibody as an Effective FRET-Based Biosensor for Progesterone Hormone Screening.

In this work, carbon dots (CDs) were synthesized by a one-step hydrothermal method using citric acid and ethylene diamine, and covalently functionalized with antibodies for the sensing of progesterone hormone. The structural and morphological analysis reveals that the synthesized CDs are of average size (diameter 8-10 nm) and the surface functionalities are confirmed by XPS, XRD and FT-IR. Further graphene oxide (GO) is used as a quencher due to the fluorescence resonance energy transfer (FRET) mechanism, whereas the presence of the analyte progesterone turns on the fluorescence because of displacement of GO from the surface of CDs effectively inhibiting FRET efficiency due to the increased distance between donor and acceptor moieties. The linear curve is obtained with different progesterone concentrations with 13.8 nM detection limits (R2 = 0.974). The proposed optical method demonstrated high selectivity performance in the presence of structurally resembling interfering compounds. The PL intensity increased linearly with the increased progesterone concentration range (10-900 nM) under the optimal experimental parameters. The developed level-free immunosensor has emerged as a potential platform for simplified progesterone analysis due to the high selectivity performance and good recovery in different samples of spiked water.

Be-original break new ground: Fluorescence sensing of humic acid in natural water and soil by pitaya seed carbon dots

Pitaya seed carbon dots (P-CDs) with good biocompatibility were synthesized by hydrothermal method using natural biological matrix as carbon source, which applied to the detection of humic acid (HA) for the first time. So far, there is no report on the use of biomatrix-derived carbon dots for the detection of HA. This method can bring less pollution to the detection process of HA, which is very important to ensure lower cost, environmental safety and minimized energy consumption. In addition, it was worth noting that, based on the concept of green chemistry, the preparation process of P-CDs is simple, and the fluorescence method is used for analysis. Based on the fluorescence resonance energy transfer (FRET) mechanism, the detection of HA in water and soil can be realized in a short time. The results matched those of high-performance liquid chromatography (HPLC), suggesting that it shows great potential in water and soil quality monitoring.

Two bis-color excited luminescent sensors of two-dimensional Cd(II)-MOFs bearing mixed ligands for detection of ions and pesticides in aqueous solutions

Two metal organic framework were constructed from mix-ligands and Cd(II) ions: [Cd(NIP)2(DTP)(H2O)2]·H2O (Cd-1) (H2NIP = 5-nitroisophthalic acid and DTP = 3,5-di(1,2,4-triazol-1-yl)pyridine) and [Cd(NTP)2(DTP)(Et)(H2O)2]·(H2O)0.5 (Cd-2) (H2NTP = nitroterephthalic acid and Et = ethanol). The MOFs were determined and confirmed by single-crystal X-ray diffraction (XRD), elemental analysis, infrared spectroscopy (IR), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and fluorescence analysis. The fluorescence sensing application of the sensors demonstrated the two sensors were extra sensitive and selective towards Fe3+ and Cr2O72- during the sensing of the ions under both 250 and 290 nm excitation wavelength; were extra effective and sensitive towards NTP (EX 250 nm) and MMT (EX 290 nm) in sensing of the pesticides for the two sensors. Mechanism investigation revealed both inner filter effect (IFE) and fluorescence resonance energy transfer (FRET) mechanisms played major roles during the sensing process of Fe3+, Cr2O72−, NTP and MMT.

Dual function naphthalimide modified mesoporous silica for organic pollutant sensing and removal from water

Dual-function materials for the selective sensing and adsorption of multiple dyes simultaneously are still challenging to prepare. Herein, a naphthalimide functionalized SBA–15 fluorescent sensor and adsorbent, namely, TPNI–SBA–15, was developed for the simultaneous detection and adsorption of the anionic dye congo red (CR) and the cationic dyes methylene blue (MLB) and malachite green (MG). The fluorescence intensity of TPNI–SBA–15 at 531 nm selectively quenched by CR, MLB and MG. The detection of CR was based on inner filter effect mechanism, and the detection of MLB and MG was attributed to the combined mechanism of electrostatic interaction, electron transfer and fluorescence resonance energy transfer. Limits of detection of 0.03, 0.10 and 0.26 μM, and limits of quantification of 0.10, 0.33 and 0.85 μM were estimated for the determination of CR, MLB and MG, respectively. The satisfactory recoveries from 99.72 to 104.80 % were acquired for detecting CR in tap water, with a relative standard deviation less than 2.9 %. Moreover, TPNI–SBA–15 can selectively remove CR, MLB and MG from water with a removal percentage reaching 100 %, 98.8 % and 61.5 %, respectively, within 1 min. TPNI–SBA–15 exhibited good dye adsorption and removal stability after three cycles of adsorption, desorption and regeneration. TPNI–SBA–15 also removes CR, MLB and MG from binary, ternary and quaternary dye mixtures conveniently and effectively. This work provided an economic strategy to realize simultaneous selective detection and adsorption of organic dyes by rationally introducing specific organic functional units into mesoporous structures. Keywords: Mesoporous silica; Organic dyes; Selective sensing; Selective adsorption.

Paper-based LRET sensor for the detection of total heavy rare-earth ions.

Based on the mechanism of luminescence resonance energy transfer (LRET) and using a special single strand DNA as the recognition element, a portable paper-based sensor for the accurate detection of total heavy rare-earth ions (mainly Gd3+, Tb3+ and Dy3+) concentration was proposed. The RNA cleaving-DNAzyme should recognize rare-earth ions to cleave RNA on DNA duplexes linking UCNPs and AuNPs, causing UCNPs and AuNPs to approach each other, inducing LRET, which attenuated the green upconversion luminescence (UCL) triggered by the 980 nm laser. UCL was captured by a charge-coupled device (CCD) image sensor and processed with the red-green-blue (RGB) image to quantitatively analyze heavy rare-earth ions in the samples. In the range of 5–50 μmol·L-1, the sensor has good sensitivity, with the limit of detection of 1.26 μmol L−1.

MnO2 Nanosheet/Polydopamine Double-Quenching Ru(bpy)32+@TMU-3 Electrochemiluminescence for Ultrasensitive Immunosensing of Alpha-Fetoprotein

In this work, we propose a novel double-quenching electrochemical luminescence (ECL) strategy; this strategy is based on the double-quenching effect of Ru(bpy)32+-functionalized three-dimensional (3D) metal–organic framework (MOF) by MnO2/PDA. An ECL immunosensor for ultrasensitive detection of alpha-fetoprotein (AFP) has been designed. TMU-3 with a rich mesoporous structure can be used to encapsulate Ru(bpy)32+, which can effectively reduce the leakage of Ru(bpy)32+. Moreover, the ultraviolet–visible (UV–vis) absorption spectrum of the lamellar MnO2/PDA nanomaterials with a nanometer scale of about 1 μm overlaps with the ECL emission spectrum of the porous bamboo leaf-like Ru(bpy)32+@TMU-3 with a nanometer scale of about 1 μm. Thus, an ECL resonance energy transfer (ECL-RET) mechanism between Ru(bpy)32+@TMU-3 (donor) and MnO2/PDA (recipient) is formed. In this way, an ECL immunosensor with a dual-quenching strategy for ECL signal is developed. In order to test the practicability of this method in clinical analysis, the detection target marker AFP content ranged from 0.01 pg/mL to 5 ng/mL and the detection limit was set to 10.7 fg/mL. In summary, this work demonstrates the detection and application of a signal-quenched ECL immunosensor and ECL immunoassay based on a luminescence-functionalized MOF system for biomarker detection. It indicates a great prospect in the analysis of other biomarkers and clinical analysis.

Self-illuminating NIR-II bioluminescence imaging probe based on silver sulfide quantum dots.

Bioluminescence (BL) imaging has emerged to tackle the potential challenges of fluorescence (FL) imaging including the autofluorescence background, inhomogeneous illumination over a wide imaging field, and the light-induced overheating effect. Taking advantage of the bioluminescence resonance energy transfer (BRET) mechanism between a conventional luciferin compound and a suitable acceptor, the visible light of the former can be extended to photons with longer wavelengths emitting from the latter. Although BRET-based self-illuminating imaging probes have already been prepared, employing potentially cytotoxic elements as the acceptor with the emission wavelengths which hardly reach the first near-infrared (NIR-I) window, has limited their applications as safe and high performance in vivo imaging agents. Herein, we report a biocompatible, self-illuminating, and second near-infrared (NIR-II) emissive probe to address the cytotoxicity concerns as well as improve the penetration depth and spatiotemporal resolution of BL imaging. To this end, NanoLuc luciferase enzyme molecules were immobilized on the surface of silver sulfide quantum dots to oxidize its luciferin substrate and initiate a single-step BRET mechanism, resulting in NIR-II photons from the quantum dots. The resulting dual modality (BL/FL) probes were successfully applied to in vivo tumor imaging in mice, demonstrating that NIR-II BL signals could be easily detected from the tumor sites, giving rise to ∼2 times higher signal-to-noise ratios compared to those obtained under FL mode. The results indicated that nontoxic NIR-II emitting nanocrystals deserve more attention to be tailored to fill the growing demands of preparing appropriate agents for high quality BL imaging.

Preparation of Polyvinyl Imine Modified Carbon Quantum Dots and Their Application in Methotrexate Detection.

Objective: A sensitive and selective fluorescence-detection platform based on carbon quantum dots (CQDs) was designed and developed for the determination of methotrexate (MTX), for the purpose of minimizing the possible toxic threat of MTX in clinics. Methods: The approach was prepared for the first time by a simple, hydrothermal method, making the synthesis and modification processes realized in one step using polyethyleneimine (PEI), and the proposed PEI-CQDs were obtained with high fluorescence quantum yield (38%). Results: MTX was found highly responsive and effective in quenching the fluorescence of the PEI-CQDs, due to a suggested fluorescence resonance energy transfer mechanism or inner-filter effect. The linear range of MTX was between 1 and 600 μmol/L under optimum conditions, with a detection limit (LOD) as low as 0.33 μmol/L. Furthermore, the fluorescent method was established for the MTX assay, and satisfactory results were acquired in real-sample determination. The average labeled quantity was 98.2%, and the average added standard recovery was 100.9%. Conclusions: The proposed PEI-CQDs showed a remarkable potential for broad applications in biological molecule determination and environmental analysis.

Novel Polarity Fluorescent Probe for Dual-Color Visualization of Lysosomes and Plasma Membrane during Apoptosis.

Apoptosis plays a crucial role in the occurrence of cancer and other diseases. Real-time monitoring of the cell apoptosis process has great significance for cell viability and drug screening. Herein, a novel fluorescent probe was constructed based on the fluorescence resonance energy transfer mechanism, which track the sensitivity of polarity changes, as well as detect the drug-induced cell apoptosis process in a dual-color mode. Importantly, the change of cellular microenvironmental polarity makes it possible to dynamically visualize the process of drug-induced cell apoptosis. More significantly, the designed probe targeted the lysosomes in the living cells to give a blue emission, and it accumulated on the plasma membrane to display red fluorescence during the drug-induced cell apoptosis process. Thus, cell viability could be monitored by both the localization and emission colors of the robust probe. We expect that the unique probe can provide a new blueprint for evaluating and screening apoptosis-related drugs.

A rod-like melem with high fluorescence quantum yield for sensitive detection of reduced glutathione

A rod-like melem with high fluorescence quantum yield of 71.3 % was prepared in this work to enhance the chemiluminescence (CL) intensity of Na2SO3-Ce (Ⅳ) system. The results showed that the CL intensity of Na2SO3-Ce (Ⅳ) system could be increased by 350 times based on chemiluminescence resonance energy transfer (CRET) mechanism. Furthermore, a CL sensor based on Na2SO3-Ce (Ⅳ)-melem system was designed to detect reduced glutathione (G-SH). It was indicated that the CL sensor exhibited excellent G-SH detection performance with a detection limit of 0.065 nM and a linear range from 0.32 to 650 μM. This study applied melem for CL detection and provided a new way for the detection of G-SH.

Tetraphenylethylene-based fluorescent conjugated microporous polymers for fluorescent sensing trinitrophenol

Two tetraphenylethylene-based fluorescent conjugated microporous polymers (TTTPT and TTDAT) were obtained by the Friedel−Crafts polymerization reactions catalysed by CH3SO3H. In virtue of containing tetraphenylethylene, triphenylamine and s-triazine units in their porous skeletons, the resulting TTTPT and TTDAT show excellent fluorescence sensing performance for trinitrophenol (TNP) with high quenching coefficients of 1.66 × 104 and 1.31 × 105 l mol–1, respectively. TTDAT can also sense to dinitrophenol (DNP) with the Ksv of 2.70 × 104 l mol–1. The fluorescent quenching mechanisms of TTTPT and TTDAT for selective detecting TNP attribute to conventional photoinduced electron-transfer mechanism, absorption competition quenching mechanism and/or the resonant energy transfer mechanism.

Fluorescent Biosensors for the Detection of Viruses Using Graphene and Two-Dimensional Carbon Nanomaterials

Two-dimensional carbon nanomaterials have been commonly employed in the field of biosensors to improve their sensitivity/limits of detection and shorten the analysis time. These nanomaterials act as efficient transducers because of their unique characteristics, such as high surface area and optical, electrical, and magnetic properties, which in turn have been exploited to create simple, quick, and low-cost biosensing platforms. In this review, graphene and two-dimensional carbon material-based fluorescent biosensors are covered between 2010 and 2021, for the detection of different human viruses. This review specifically focuses on the new developments in graphene and two-dimensional carbon nanomaterials for fluorescent biosensing based on the Förster resonance energy transfer (FRET) mechanism. The high-efficiency quenching capability of graphene via the FRET mechanism enhances the fluorescent-based biosensors. The review provides a comprehensive reference for the different types of carbon nanomaterials employed for the detection of viruses such as Rotavirus, Ebola virus, Influenza virus H3N2, HIV, Hepatitis C virus (HCV), and Hepatitis B virus (HBV). This review covers the various multiplexing detection technologies as a new direction in the development of biosensing platforms for virus detection. At the end of the review, the different challenges in the use of fluorescent biosensors, as well as some insights into how to overcome them, are highlighted.

Facile off-on fluorescence biosensing of human papillomavirus using DNA probe coupled with sunflower seed shells carbon dots

We report a fluorescent “off-on” platform based on carbon dots (CDs) and DNA probe to achieve trace detection of human papillomavirus 16 (HPV 16). Initially, the CDs was synthesized by simple two-step method, using biomass sunflower seed shells as precursor, doped with L-arginine and passivated by polyethyleneimine (PEI) to obtain positively charged biomass CDs that had the merits of high fluorescence intensity, green synthesis and good stability. Then, the DNA probe was prepared by modifying single-stranded DNA (ssDNA) with 4-(4-dimethylaminobenzazo) benzoyl (Dabcyl) fluorescence quenching agent. Due to electrostatic effect and Förster resonance energy transfer (FRET) mechanism, DNA probe can cause fluorescence quenching of the prepared CDs. Since HPV 16 bound to the DNA probe followed a strict base complementation pairing rule, it turned on the fluorescence of CDs by separating the DNA probe from the CDs. The limit of detection (LOD = 0.47 nM) and the linear range (0.5–150 nM) of the probe for HPV 16 were favorable. The recovery of HPV 16 in urine and cervical swabs were 96.6%-113.3% and 95.7%-103.9%. This method can achieve highly specific detection of the DNA sequences of target virus without complicated operation and expensive equipment, which is of great significance for biochemical analysis.

Rational design of a turn-on fluorescent probe for visualization of GRP78 protein in tumor models

Fluorescence image for accurate tumor label still faces challenges in cancer detection and diagnostics. Emerging evidence is indicating that glucose-regulated protein 78 (GRP78), a stress-inducible protein chaperone, is a great potential biomarker and therapeutic target for cancer. However, currently available probe for image tumor based on GRP78 has not been reported, owning to no obvious strategy in probe design towards this protein. In this paper, a hairpin-shaped peptidyl probe (pepFAM) conjugated with a 5-FAM fluorophore and a dabcyl quencher at both ends was developed, respectively. The probe was designed by performing a traditional fluorescence resonance energy transfer mechanism and employing a GRP78 specifically-binding peptide. Furthermore, the probe was used to specifically image cancer cells, and accurately image xenograft tumors in mice models. The novel fluorescent probe is expected to be a useful tool for the diagnostics of cancer.

Novel Electrochemical Synthesis and Characterization of Zn(II) Metal Organic Framework for Photo-catalytic and Sensing Applications.

Multidentate 1,3,5-benzenetricarboxylic acid (organic linker), Zn (II) based Zn-BTC has been synthesized via electrochemical method. Quantitative and Qualitative analyses of synthesized metal-organic framework (MOF) have been done using Fourier Transform Infrared (FTIR) Spectroscopy, Energy Dispersive X- Ray Spectroscopy (EDS), and Photoluminescence (PL). Powder X-Ray Diffraction (PXRD) and Scanning Electron Microscopy (SEM) have been used for crystallographic and morphological & topographical analyses, respectively. Crystallographic studies confirm the formation of face-centered cubic (fcc) crystal structure with good crystallinity. Photo-catalytic activity of synthesized MOF has been tested using Methylene Blue (MB) dye as a test contaminant in aqueous media under sunlight irradiation. Recorded results reveal that the synthesized MOF efficiently degrade MB dye upto 96% under sunlight exposure after 270min. Photoluminescence studies indicate that Zn-BTC could be used as an efficient material for sensing of nitroaromatic compounds (NACs): 4-Nitroaniline (4-NA), 2-Nitroaniline (2-NA), 3- Nitroaniline (3-NA), 2,4-Dinitrotoulene (2,4-DNT), 4-Nitrotoulene (4-NT) in N,N'-Dimethylformamide (DMF) by fluorescence quenching and shows maximum quenching efficiency towards 3-NA (72.80%). Notably, the variation in luminescence intensity of 3-NA@Zn-BTC shows a linear relationship over its different concentrations from 0-1000ppb range with KSV = 2.7 × 104M-1 and R2 = 0.9924 with limit of detection 0.889ppb (6.43µM) (LOD). The possible ways of luminescence quenching are successfully explained by the combination of Photoinduced Electron Transfer (PET) and Resonance Energy Transfer (RET) mechanisms. Additionally, the Density Functional Theory (DFT) calculations have been employed to support the experimental results. Zn-BTC fully demonstrates the power of a multi component MOF, which provides a feasible pathway for the design of novel material towards fast responding luminescence sensing and photocatalytic degradation of pollutants.

Aptamer functionalization and high-contrast reversible dual-color photoswitching fluorescence of polymeric nanoparticles for latent fingerprints imaging

Exploiting the intelligent stimuli-responsive fluorescent materials, which can selectively recognize lysozyme in fingerprints and enable high-contrast imaging, is still a challenge in latent fingerprints (LFPs) detection. Herein, based on Fluorescence Resonance Energy Transfer (FRET) mechanism, aptamer functionalization and high-contrast reversible dual-color photoswitching fluorescence of polymeric nanoparticles (LBA-RPFPNs) have been successfully constructed for efficient imaging of LFPs. Experiments results showed that LBA-RPFPNs displayed good water dispersibility, fast photo-responsiveness, favorable photoreversibility and good long-term stability. Of note, the aptamer possessed the ability of LBA-RPFPNs to target lysozyme in LFPs, thus realizing the selectivity of LFPs. Furthermore, the fluorescence of LBA-RPFPNs was reversibly switched between green and red through UV/visible light, achieving for high-contrast imaging of LFPs. This strategy provides good potential in disclosing the valuable information within LFPs.

Highly conjugated carbazole and pyrrolo[1,2-a]quinoxaline based small molecules for fluorescent detection of nitroexplosives

Explosive detection has been a need of the current times to ensure security of people & fluorescent small molecules have become popular for their rapid and selective detection. Herein, we report two highly conjugated small organic fluorophores i.e.1,3,6,8-tetraethynyl-9-hexyl-9H-carbazole (Tetra) based on carbazole & 5-(4′-(pyrrolo[1,2-a]quinoxalin-4-yl)-[1,1′-biphenyl]-4-yl)pyrrolo[1,2-c]quinazoline (PQ-1) based on pyrroloquinoxaline scaffolds, both of which showed excellent quenching of fluorescence in the presence of nitroexplosive molecules. Linear Stern Volmer plots were obtained with different quencher molecules giving low detection limits even under visual inspection. A spectral overlap between the absorption spectra of picric acid (PA) and emission spectra of Tetra and a decrease in fluorescence lifetime of fluorophore with increasing concentration of quencher molecules confirm dynamic quenching with Forster Resonance Energy Transfer (FRET) mechanism. PQ-1 on the other hand showed a static mode of quenching indicated by no change in fluorescence lifetimes. DFT studies were done to identify the HOMO-LUMO bandgap, which are in good agreement with the experimental photophysical properties of the molecules. A low detection limit of 6.68 × 10−7 M for picric acid & 2.53 × 10−6 M for 2,4,6-TNT was observed using Tetra. Similarly, detection limit of 4.45 × 10−6 M & 1.84 × 10−6 M was found for PQ-1 towards picric acid & 2,4,6-TNT respectively. Interestingly, both Tetra & PQ-1 sensed aliphatic nitrocompounds like nitromethane with low detection limits of 4.57 × 10−7 M & 9.37 × 10−7 M respectively.