Upconversion Fluorescence Resonance Energy Transfer Research Articles

Full-Spectrum Utilization of ZIF-67/Ag NPs/NaYF4:Yb,Er Photocatalysts for Efficient Degradation of Sulfadiazine: Upconversion Mechanism and DFT Calculation.

In this work, novel ternary composite ZIF-67/Ag NPs/NaYF4:Yb,Er is synthesized by solvothermal method. The photocatalytic activity of the composite is evaluated by sulfadiazine (SDZ) degradation under simulated sunlight. High elimination efficiency of the composite is 95.4% in 180min with good reusability and stability. The active species (h+, ·O2 - and ·OH) are identified. The attack sites and degradation process of SDZ are deeply investigated based on theoretical calculation and liquid chromatography-mass spectrometry analysis. The upconversion mechanism study shows that favorable photocatalytic effectiveness is attributed to the full utilization of sunlight through the energy transfer upconversion process and fluorescence resonance energy transfer. Additionally, the composite is endowed with outstanding light-absorbing qualities and effective photogenerated electron-hole pair separation thanks to the localized surface plasmon resonance effect of Ag nanoparticles. This work can motivate further design of novel photocatalysts with upconversion luminescence performance, which are applied to the removal of sulphonamide antibiotics in the environment.

A homogeneous biosensor for carbohydrate antigen 153 detection in human serum based on upconversion fluorescence resonance energy transfer

Quantitative determination of carbohydrate antigen 153 (CA153) in human serum plays an important role in early diagnosis of breast cancer. In this work, a highly sensitive and selective biosensor for CA153 detection was developed based on a fluorescent resonance energy transfer (FRET) strategy, in which near-infrared (NIR)-excitable upconversion nanoparticles (UCNPs) and the commercial organic dye, FAM, were employed as energy donor and energy acceptor, respectively. The two components were linked by a molecular beacon (MB) containing CA153 aptamer sequence and the upconversion fluorescence (UCF) of UCNPs can be effectively quenched by FAM. In presence of CA153, the hairpin structure was opened, resulting in the separation of UCNPs and FAM and the inhibition of FRET. The UCF showed a linear relationship with the logarithm of CA153 concentration in the range from 0.01 to 150 U/mL, with a LOD of 4.5 mU/mL in HEPES buffer. This probe can be successfully applied for CA153 assay in human serum, which may be a useful tool for early diagnosis of breast cancer.

“Off-On” typed upconversion fluorescence resonance energy transfer probe for the determination of Cu2+ in tap water

Detection of copper plays a prominent role in the environmental protection and human health. Herein, we firstly design and construct an “off–on” upconversion fluorescence resonance energy transfer (UFRET) probe with low toxicity for the Cu2+ determination by using NaYF4: Yb3+, Er3+ upconversion nanoparticles (UCNPs) and Au NPs. UCNPs with positive charge and Au NPs with negative charge are respectively employed as the donor and acceptor, and bound together to form UFRET probe. The upconversion fluorescence quenching of UCNPs occurs by Au NPs through FRET (defined as “off” state). When Cu2+ exists in samples, Cu2+ reacts with 4-mercaptobenzoic acid (4-MBA) capped on the surface of Au NPs to make Au NPs detach from UCNPs, leading to the termination of FRET and the recovery of upconversion fluorescence (defined as “on” state). “Off-on” typed UFRET probe has excellent sensing performances, including linear range of 0.02–1 μM Cu2+ concentration, the limit of detection of 18.2 nM, high selectivity to Cu2+ and good recovery. The probe has been successfully used to determine Cu2+ in spiked tap water with satisfactory results. The probe will provide theoretical and technical support for the design of new sensitive heavy metal ion detection probe.

Upconversion nanoparticles-based FRET system for sensitive detection of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a pathogenic bacterium that seriously endangers food safety. Herein, a rapid, sensitive and specific aptasensor based on upconversion fluorescence resonance energy transfer (FRET) was developed for S. aureus detection in food. Aptamer-functionalized gold nanoparticles (AuNPs-aptamers) were bonded to cDNA-modified upconversion nanoparticles (UCNPs-cDNA) by complementary pairing, resulting in fluorescence quenching. After adding S. aureus into the system, the aptamers preferentially combined with S. aureus, dissociated UCNPs-cDNA from AuNPs-aptamers, and the fluorescence was recovered. Under optimized conditions, there was a significant linear correlation between fluorescence intensity and S. aureus concentration over the range 47–4.7 × 107 CFU/mL (R2 = 0.9904) with a detection limit of 10.7 CFU/mL. Furthermore, the precision and accuracy of the developed biosensor were validated using standard plate count method, yielding no significant differences. The proposed method has potential application for rapid and sensitive quantification of S. aureus in food.

A highly sensitive aptasensor for vascular endothelial growth factor based on fluorescence resonance energy transfer from upconversion nanoparticles to MoS2 nanosheets.

A novel sensitive aptasensor for vascular endothelial growth factor-165 (VEGF165) was constructed based on fluorescence resonance energy transfer (FRET) by employing upconversion nanoparticles (UCNPs) and MoS2 nanosheets as the energy donor and acceptor, respectively. The upconversion fluorescence resonance energy transfer (UC-FRET) was triggered by the physical adsorption interaction between the aptamer and MoS2 nanosheets, leading to a remarkable quenching of UCNP fluorescence up to 95%. Upon addition of VEGF165 to the UCNP-aptamer system before MoS2 nanosheets were added, the aptamer preferentially bound to VEGF165 with the change of spatial conformation, which weakened the van der Waals' force between the MoS2 nanosheets and the aptamer, thus leading to the separation of the donor and the acceptor. Consequently, the FRET phenomenon was inhibited and the luminescence of UCNPs was regained, which was linearly related to the concentration of VEGF165 in the range of 0.1 ng mL-1 to 16 ng mL-1. By taking advantage of the extreme fluorescence quenching ability of MoS2 nanosheets and the optical merits of UCNPs, the aptasensor based on UC-FRET exhibited favorable performance for the homogeneous assay of VEGF165 in human serum, which is of great value for clinical diagnosis of tumors and related biological studies.

A novel arginine bioprobe based on up-conversion fluorescence resonance energy transfer

Arginine is an important amino acid in humankind bodies and is of essential clinical significance. This paper presents a novel bioprobe based on fluorescence resonance energy transfer (FRET), which can be used to detect arginine efficiently and economically. In this bioprobe system, positively charged up-conversion phosphor NaYF4 (NYF) acts as energy donor, and negatively charged gold nanoparticle (AuNP) acts as energy acceptor. The oppositely charged donor and acceptor come into close proximity through electrostatic attraction effect, which results in the occurrence of FRET between NYF and AuNP. The FRET process is thus in the “on” state, meanwhile the system is in the “off” state, and the emitting light of NYF quenched. When positively charged arginine is added into the system, the guanidyl of arginine binds to AuNP and leads to the negatively charged AuNP becomes positively charged one, and the AuNP separates from NYF because of the electrostatic repulsion. The FRET process is blocked and the system switches to the “on” state because the distance between NYF and AuNP becomes longer. In the “on” state, the intensity of the restored emitting light is proportional to the concentration of arginine. This approach brings a good linear relationship between the fluorescence intensity and the concentration of arginine in the concentration range of 14.42–115.04 μM. The limit of detection is as low as 2.9 μM. A new method for quantitative determination of arginine by just measuring the fluorescence intensity of the system is established.

A novel up-conversion fluorescence resonance energy transfer sensor for the high sensitivity detection of coumarin in cosmetics

Coumarin is widely used as spices in a variety of cosmetics. However, its concentration in cosmetics is strictly limited because it is a kind of suspected carcinogen. It is essential and highly desired to develop fast and convenient detection methods to detect trace amount of coumarin. This work presents a novel and simplified fluorescent sensor for the determination of coumarin based on the phenomenon of fluorescence resonance energy transfer (FRET). In this system, the NaYF4: Yb,Er (NaYF) behaves as energy donor, and the rhodamine 6 G (Rh6 G) behaves as energy receptor. The β-cyclodextrin (CD) was modified on NaYF and was used to ensure the selectivity towards coumarin and to bring the donor and receptor into FRET proximity through specific host-guest interaction, which is different from the previously reported FRET models that either rely on π-π stacking interaction or rely on molecular recognition. This fluorescent sensor shows high sensitivity and selectivity toward coumarin, and the linear response range is 2.5–32.5 μM with a limit of detection as low as 0.74 μM.

Rhodamine B derivative-modified up-conversion nanoparticle probes based on fluorescence resonance energy transfer (FRET) for the solid-based detection of copper ions.

Herein, a novel solid-based up-conversion fluorescence resonance energy transfer (FRET) sensor was developed using rhodamine B hydrazide, which provided a selective fluorescence response and suitable affinity towards Cu2+ ions over other biologically relevant metal ions because the Cu2+ ion could promote the hydrolysis of α-amino acid esters of rhodamine B hydrazide and yield the Cu·α-amino acid chelate. This solid-based detection system is more convenient for the detection of Cu2+ based on color change and emission spectra instead of the complicated and tedious measurements than other up-conversion sensors and up-conversion luminescent nanoparticles used as an excitation source; moreover, the proposed system shows high selectivity, minimum photo-damage to living organisms, and high chemical stability.

An ultrasensitive homogeneous aptasensor for carcinoembryonic antigen based on upconversion fluorescence resonance energy transfer

Carcinoembryonic antigen (CEA) has been recognized as one of the most important tumor markers. Herein, we reported an ultrasensitive homogeneous aptasensor based on fluorescence resonance energy transfer (FRET) between upconversion nanoparticles (UCNPs) and graphene oxide (GO) for CEA detection. The CEA aptamer modified UCNPs can bind to the surface of GO through π-π stacking interaction, resulting in fluorescence quenching due to the energy transfer from UCNPs to GO. After the introduction of CEA, the CEA aptamer preferentially combined with CEA to form three-dimensional structure which made UCNPs-aptamer dissociate from the GO, blocking the energy transfer process. The fluorescence of UCNPs was accordingly restored in a CEA concentration-dependent manner both aqueous solution and human serum samples. The aptasensor could monitor CEA level directly in human serum and the results were strongly correlated with commercial chemiluminescence kits. The excellent detection performance suggested promising prospect of the aptasensor in practical application.

Paper-based upconversion fluorescence resonance energy transfer biosensor for sensitive detection of multiple cancer biomarkers.

A paper-based upconversion fluorescence resonance energy transfer assay device is proposed for sensitive detection of CEA. The device is fabricated on a normal filter paper with simple nano-printing method. Upconversion nanoparticles tagged with specific antibodies are printed to the test zones on the test paper, followed by the introduction of assay antigen. Upconversion fluorescence measurements are directly conducted on the test zones after the antigen-to-antibody reactions. Furthermore, a multi-channel test paper for simultaneous detection of multiple cancer biomarkers was established by the same method and obtained positive results. The device showed high anti-interfere, stability, reproducible and low detection limit (0.89 ng/mL), moreover it is very easy to fabricate and operate, which is a promising prospect for a clinical point-of-care test.

Upconversion fluorescence resonance energy transfer—a novel approach for sensitive detection of fluoroquinolones in water samples

A novel homogeneous assay method was put forth for simultaneous sensing of fluoroquinolone derivatives (FQs) in water utilizing the upconversion fluorescence resonance energy transfer (FRET) process based on the competitive reaction between dissolved FQs and labeled AuNPs for FQs Mab connected UCPs. The prepared size-tunable β-NaLuF4:Yb,Er,Gd upconversion phosphors (UCPs) were functionalized with carboxylic acid (COOH–) and monoclonal antibody (Mab, C2F3C2) to act as a donor. The gold nanoparticles (AuNPs) labeled with the corresponding antigen (ciprofloxacin-BSA) take the role of an acceptor. Under optimized conditions, the limit of detections (LODs) for three common FQs, enrofloxacin (ENR), ciprofloxaxin (CIP), and norfloxacin (NOR), were 0.19–0.32ng/mL based on 3σ. The recoveries were found to be in the range of 73.5–114.5% (normalized value according to the cross-reactivity of Mab) for water samples (tap water, pond water and river water). The proposed approach possesses significant advantages as follows: (i) simple procedure (only one step) without washing and separation steps, and no sample pretreatment other than filtration; (ii) fast liquid-phase kinetics with shortened incubation time; and (iii) high tolerance to various interfering substances. All of which indicated its potentiality as an efficient biosensor towards the monitoring of FQs in aquatic environments.

NaYF4:Yb3+–Er3+ nanocrystals/P(NIPAM-co-RhBHA) core–shell nanogels: Preparation, structure, multi stimuli-responsive behaviors and application as detector for Hg2+ ions

Abstract In the present study, we report a novel core–shell nanogels of NaYF 4 :Yb 3+ –Er 3+ nanocrystals/P(NIPAM- co -RhBHA) based on up-conversion excitation and fluorescence resonance energy transfer (FRET). Firstly, up-conversion NaYF 4 :Yb 3+ –Er 3+ nanocrystals were synthesized by hydrothermal method with EDTA, Er(NO 3 ) 3 , Yb(NO 3 ) 3 , Y(NO 3 ) 3 and NaF as raw materials. Then, the nanocrystals were decorated with MPS. Finally, core–shell nanogels with thermo-responsive shells were fabricated via free radical emulsion polymerization of N -isopropylacrylamide (NIPAM) and N -acrylyl- N ′-rhodamine B acylhydrazine thiourea (RhBHA) dye monomers. Their structure, stimuli-responsive behaviors were investigated via TEM, FTIR, XRD, DSC, UV–vis and PL in detail. The results suggest that the nanogels can response to multi-stimuli, such as pH value, temperature, metal ions, and they can be used as sensitive detector for Hg 2+ ions.

An upconversion fluorescence resonance energy transfer nanosensor for one step detection of melamine in raw milk

Here we report a nanosensor based on fluorescence resonance energy transfer (FRET) between upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs) for melamine detection. The positively charged UCNPs as donor and the negatively charged AuNPs as acceptor bound together through electrostatic interaction, which caused the fluorescence quenching of UCNPs. Upon addition of melamine, AuNPs were released from the surface of UCNPs and aggregation due to the N-Au interaction between melamine and AuNPs, which results in the fluorescence of UCNPs gradually recovered. Under the optimal conditions including media pH (7.0), the concentration of AuNPs (1.23nM) and incubation time (12min), the fluorescence enhanced efficiency shows a linear response to the melamine concentration ranging from 32.0 to 500nM with a detection limit of 18.0nM. Compared with other fluorescence methods, the fluorimetric nanosensor shows high sensitivity of 0.968, ease of operation and can be used for the determination of melamine in raw milk samples.

An aptasensor for carcinoembryonic antigen based on upconversion fluorescence resonance energy transfer

In this work, an aptasensor for carcinoembryonic antigen (CEA) determination was constructed on the basis of fluorescence resonance energy transfer (FRET) between upconversion phosphors (UCPs) and carbon nanoparticles (CNPs). Polyacrylic acid (PAA)-capped UCPs (NaYF4:Yb, Er) were employed as the energy donor, which were covalently tagged with an amino group modified CEA aptamer (5′-NH2-(A)5 ATA CCA GCT TAT TCA ATT-3′). The fluorescence of UCPs was dramatically quenched by CNPs due to the π–π stacking interaction between CEA aptamer and CNPs, which brought UCPs and CNPs in close proximity and triggered the energy transfer from UCPs to CNPs. When the CEA protein was introduced into the UCPs–aptamer–CNPs complex, the CEA aptamer preferentially interacted with CEA protein, leading to a structural change of the aptamer which was unfavorable for the π–π stacking. As a result, the energy transfer process was blocked and the fluorescence of UCPs was recovered. The degree of fluorescence restoration linearly depended on CEA concentration in the range of 0.1–40ng/mL in both buffer solution and human serum samples. The aptasensor exhibited high specificity toward CEA protein without being interfered by other biomolecules. The proposed method showed the potential of clinical applications because of the good sensing performance and ease of operation.

Determination of Salmonella typhimurium by a Fluorescence Resonance Energy Transfer Biosensor Using Upconversion Nanoparticles as Labels

A Salmonella typhimurium (S. typhimurium) biosensor based on a fluorescence resonance energy transfer between upconversion and gold nanoparticles is reported. NaYF4:Yb,Er nanoparticles were synthesized and modified with a S. typhimurium target DNA complementary sequence to form the sensor. Gold nanoparticles were modified with a S. typhimurium target DNA complementary sequence to constitute the quenching probe. In the presence of S. typhimurium target DNA, gold and upconversion nanoparticles formed a sandwich complex, and the upconversion fluorescence resonance energy transfer occurred. Under the optimal conditions, the relative fluorescence was proportional to the concentration of S. typhimurium target DNA in the range of 0.001 pmol/L to 1 pmol/L with a limit of detection of 1 fM. S. typhimurium was detected from 30 cfu/mL to 5150 cfu/mL with a detection limit of 3 cfu/mL. The procedure was successfully applied to determine S. typhimurium in milk and validated by a traditional plate counting method. The developed upconversion fluorescence resonance energy transfer method is simple, fast, sensitive, specific, and incorporates nanomaterials in biosensor design.

Upconversion fluorescence resonance energy transfer biosensor for sensitive detection of human immunodeficiency virus antibodies in human serum

A facile one-step approach was proposed to prepare hydrophilic and peptide-functionalized upconversion nanoparticles (UCNPs), which were used in the design of a biosensor for the sensitive and selective determination of human immunodeficiency virus antibodies in human serum based on FRET from the UCNPs to the graphene oxide.

An ultrasensitive homogeneous aptasensor for kanamycin based on upconversion fluorescence resonance energy transfer

We developed an ultrasensitive fluorescence resonance energy transfer (FRET) aptasensor for kanamycin detection, using upconversion nanoparticles (UCNPs) as the energy donor and graphene as the energy acceptor. Oleic acid modified upconversion nanoparticles were synthesized through a hydrothermal process followed by a ligand exchange with hexanedioic acid. The kanamycin aptamer (5'-NH2-AGATGGGGGTTGAGGCTAAGCCGA-3') was tagged to UCNPs through an EDC–NHS protocol. The π–π stacking interaction between the aptamer and graphene brought UCNPs and graphene in close proximity and hence initiated the FRET process resulting in quenching of UCNPs fluorescence. The addition of kanamycin to the UCNPs–aptamer–graphene complex caused the fluorescence recovery because of the blocking of the energy transfer, which was induced by the conformation change of aptamer into a hairpin structure. A linear calibration was obtained between the fluorescence intensity and the logarithm of kanamycin concentration in the range from 0.01nM to 3nM in aqueous buffer solution, with a detection limit of 9pM. The aptasensor was also applicable in diluted human serum sample with a linear range from 0.03nM to 3nM and a detection limit of 18pM. The aptasensor showed good specificity towards kanamycin without being disturbed by other antibiotics. The ultrahigh sensitivity and pronounced robustness in complicated sample matrix suggested promising prospect of the aptasensor in practical applications.

Polyacrylic Acid Modified Upconversion Nanoparticles for Simultaneous pH-Triggered Drug Delivery and Release Imaging

A poly(acrylicacid)-modified NaYF4:Yb, Er upconversion nanoparticles (PAA-UCNPs) with dual functions of drug delivery and release imaging have been successfully developed. The PAA polymer coated on the surface of UCNPs serve as a pH-sensitive nanovalve for loading drug molecules via electrostatic interaction. The drug-loading efficiency of the PAA-UCNPs was investigated by using doxorubicin hydrochloride (DOX) as a model anticancer drug to evaluate their potential as a delivery system. Results showed loading and releasing of DOX from PAA-UCNPs were controlled by varying pH, with high encapsulation rate at weak alkaline conditions and an increased drug dissociation rate in acidic environment, which is favorable for construct a pH-responsive controlled drug delivery system. The in vitro cytotoxicity test using HeLa cell line indicated that the DOX loaded PAA-UCNPs (DOX@PAA-UCNPs) were distinctly cytotoxic to HeLa cells, while the PAA-UCNPs were highly biocompatible and suitable to use as drug carriers. Furthermore, the upconversion fluorescence resonance energy transfer (UFRET) imaging through the two-photon laser scanning microscopy (TLSM) revealed the time course of intracellular delivery of DOX from DOX@PAA-UCNPs. Thus, PAA-UCNPs are effective for constructing pH-responsive controlled drug delivery systems for multi-functional cancer therapy and imaging.

Upconversion Fluorescence Resonance Energy Transfer Biosensor with Aromatic Polymer Nanospheres as the Lable-Free Energy Acceptor

We report a new upconversion fluorescence resonance energy transfer (UC-FRET) biosensor using poly-m-phenylenediamine (PMPD) nanospheres as the energy acceptor in this paper. A single-stranded DNA (ssDNA) tagged with a sulfydryl group at the 5'-terminus was covalently linked to poly(ethylenimine) (PEI) functionalized upconversion phosphors (UCPs, the energy donor). Because of the π-rich electronic structure of PMPD, self-assembly of the donor and the acceptor was achieved through the π-π stacking interaction between ssDNA and PMPD. The fluorescence of the donor was quenched by the acceptor in a PMPD-concentration-dependent manner. A maximum quenching degree of 90% was acquired, which was among the highest levels of all previous reports. Upon the formation of double-stranded DNA (dsDNA) between the target DNA and the probe DNA, the energy acceptor was separated from the donor due to the weakened interaction between dsDNA and PMPD. The fluorescence of UCPs was accordingly restored, and a linear response was obtained with the target concentration ranging from 0.1 to 6.0 nM. The limit of detection was calculated as 0.036 nM, which was a highly competitive sensitivity. The sensor also showed high precision, pronounced specificity, and the applicability to complicated sample matrix (human serum). The UCPs-PMPD FRET sensing platform takes advantages of both the optical merits of the upconversion donors and the superquenching ability and good water-solubility of the aromatic polymer nanoparticles. This study will open the opportunity to develop a new class of UC-FRET biosensors.

Upconversion nanoparticle-based fluorescence resonance energy transfer assay for Cr(III) ions in urine

A novel assay of chromium(III) ion based on upconversion fluorescence resonance energy transfer was designed and established. Lysine-capped NaYF4:Yb/Er upconversion nanoparticles (UCNPs) and dimercaptosuccinic acid-capped gold nanoparticles (AuNPs) were used as the energy donor and acceptor, respectively. They were bound together via electrostatic interaction, resulting in the quenching of the fluorescence of UCNPs by AuNPs. Chromium(III) ions can specifically and strongly interact with dimercaptosuccinic acid that was modified on the surface of AuNPs, leading to the separation of AuNPs from UCNPs and the recovery of fluorescence of UCNPs. The fluorescence recovery of UCNPs showed a good linear response to Cr3+ concentration in the range of 2–500nM with a detection limit of 0.8nM. This method was further applied to determine the levels of Cr3+ in urine. Compared with other fluorescence methods, current method displayed very high sensitivity and signal-to-noise ratio because of the excitation of near-infrared that can eliminate autofluorescence, providing a promising examination of biological samples for the diagnostic purposes.