Fluorescence Resonance Energy Transfer Efficiency Research Articles

Smartphone-assisted fluorimetric and colorimetric dual-recognition sensing platform based on nitrogen-doped carbon dots for visual monitoring of acid red 18 in food

The widespread presence of acid red 18 (AR18) in the environment has raised concerns about the potential risks on human health and ecosystems. Herein, upon addition of AR18, nitrogen- doped carbon dots (N-CDs) synthesized with catechol and 3, 3-diaminobenzidine exhibit interactive behavior with AR18. Therein, the emission peaks at 490 nm and 410 nm are quenched by internal filtering effect (IFE) and fluorescence resonance energy transfer (FRET). Notably, the former experiences a rapid decline due to robust FRET efficiencies. On this basis, a N-CDs-based fluorimetric and colorimetric sensor is developed for sensitive and selective detection of AR18 in concentrations ranging from 0.053 to 100 μM with a low detection limit (LOD) of 53 nM. In addition, a smartphone-based dual-recognition device, integrated with composite film that enhances liquid collection in determination zone, is aimed at the sensitive detection of AR18 in food samples. The LODs are determined to be 131 nM and 122 nM respectively under fluorimetric and colorimetric conditions. Concomitantly, the device exhibits satisfying accuracy and precision for practical applications. Therefore, this newly developed dual-recognition device provides reliable means to detect the presence of AR18, demonstrating promising potential for on-site monitoring and intelligent sensing applications.

Dansyl-tagged xanthate ester as a capping agent to synthesize fluorescent silver nanoparticles with binding affinity toward serum albumin.

Developing multifunctional nanomaterials with distinct photochemical properties, such as high quantum yield, improved photostability, and good biocompatibility is critical for a wide range of biomedical applications. Motivated by this, we designed and synthesized a dansyl-tagged xanthate-based capping agent (DX) for the synthesis of fluorescent silver nanoparticles (AgNPs). The capping agent DX was characterized by 1 H and 13 C-NMR, LC-MS, and FT-IR. The synthesized DX-capped fluorescent AgNPs were thoroughly characterized by UV-visible spectroscopy, fluorescence spectroscopy, field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), dynamic light scattering (DLS), and zeta potential. The fluorescent AgNPs showed distinct surface plasmon resonance absorption at λmax = 414 nm, fluorescence at λmax = 498 nm, quantum yield = 0.24, zeta potential = +18.6 mV, average size = 18.2 nm. Furthermore, the biological activity of the fluorescent AgNPs was validated by its interaction with the most abundant protein in the blood, that is, BSA (Bovine serum albumin) and HSA (Human serum albumin) with binding constant of 2.34 × 104 M-1 and 2.14 × 104 M-1 respectively. Interestingly, fluorescence resonance energy transfer (FRET) was observed between the fluorescent AgNPs and BSA/HSA with a FRET efficiency of 77.23% and 56.36%, respectively, indicating strong interaction between fluorescent AgNPs and BSA/HSA.

A novel lanthanide metal‐organic frameworks as a luminescent sensor for efficient detection of riboflavin

Rational design of highly sensitive and rapid fluorescent probes is a major concern of analytical methods. Here, we synthesized two Ln‐PFTA with different metal nodes (Dy, Sm) by simple hydrothermal self‐assembly using 3‐fluorobiphenyl‐3′,4,5′‐tricarboxylic acid (H2PFTA) as ligand. As a ratio sensor for detecting riboflavin (RF), it has self‐calibration effect, ultra‐low detection limit (0.225 nM), excellent durability, and high selectivity. In order to add practicality, even in actual samples (fetal bovine serum, tablets, and milk), the recovery rate is as high as 92%–104%, which is considered to be an excellent luminescent sensor for detecting RF. According to the survey, there are few studies on the detection of RF by fluorescence spectroscopy. In addition, there is fluorescence resonance energy transfer (FRET) between the processes of Ln‐PFTA detecting RF, and the peak intensity change of Ln‐PFTA is attributed to its modulated luminescence characteristics. At the same time, it also shows the best FRET efficiency for detecting RF.

Overlapping characteristics of weak interactions of two transcriptional regulators with WDR5

The WD40 repeat protein 5 (WDR5) is a nuclear hub that critically influences gene expression by interacting with transcriptional regulators. Utilizing the WDR5 binding motif (WBM) site, WDR5 interacts with the myelocytomatosis (MYC), an oncoprotein transcription factor, and the retinoblastoma-binding protein 5 (RbBP5), a scaffolding element of an epigenetic complex. Given the clinical significance of these protein-protein interactions (PPIs), there is a pressing necessity for a quantitative assessment of these processes. Here, we use biolayer interferometry (BLI) to examine interactions of WDR5 with consensus peptide ligands of MYC and RbBP5. We found that both interactions exhibit relatively weak affinities arising from a fast dissociation process. Remarkably, live-cell imaging identified distinctive WDR5 localizations in the absence and presence of full-length binding partners. Although WDR5 tends to accumulate within nucleoli, WBM-mediated interactions with MYC and RbBP5 require their localization outside nucleoli. We utilize fluorescence resonance energy transfer (FRET) microscopy to confirm these weak interactions through a low FRET efficiency of the MYC-WDR5 and RbBP5-WDR5 complexes in living cells. In addition, we evaluate the impact of peptide and small-molecule inhibitors on these interactions. These outcomes form a fundamental basis for further developments to clarify the multitasking role of the WBM binding site of WDR5.

Dynamically photo-tunable multicolor luminescence of supramolecular gel based on fluorescent gelator and used for information encryption

The ingenious collaboration of photo-isomerized molecules and luminescent gelator can create self-supporting materials used for multi-level and multi-dimensional information encryption. Herein, a supramolecular gel (SDTD) was prepared by using photoluminescent gelator 1,3:2,4-di(benzylidene)-D-sorbitol (DBS), lanthanide ions (Tb3+), as well as reversible photo-isomerized diarylethylene (DTE), and spiropyran (SP) derivative. Rheological studies showed that the prepared SDTD gel possessed good self-supporting ability owing to the 3D network structure formed by DBS aggregates. Additionally, SDTD gel displayed dynamic multicolor luminescence due to the presence of three luminescent centers including DBS, Tb3+, and MC-o (the photoisomer of SP). The luminescent color of SDTD gel can be easily tuned by irradiation wavelengths and time. It was found that a photo-tunable fluorescence resonance energy transfer (FRET) occurred between Tb3+ and MC-o, Tb3+ and DTE-c (the photoisomer of DTE), the corresponding FRET efficiency was 47 % and 52 %, respectively. The results also indicated that the photo-tunable inner filter effect (IFE) occurred between DBS and DTE-c, DBS and MC-o, respectively, which endowed SDTD gel with dynamically photo-tunable multicolor luminescence capability. SDTD gel has the advantages of simple preparation, low cost, and flexible luminescence regulation. In addition, based on the multicolor luminescence of SDTD gel, a new method of multi-dimensional information encryption was proposed, which shows a potential application in the field of anti-counterfeiting materials.

Applications of Optical Method As an Effective Platform for Progesterone Sensing Using Carbon Dots and Graphene Oxide

Today, ‘Hormonal imbalance’ is a significant concern worldwide that lead to various types of complications in human body. For instance, abnormal levels of steroid hormones, such as progesterone are associated with irregular or absent menstrual periods, reproductive disorders, infertility, cardiovascular diseases, and cancer. Nowadays, progesterone is being excessively consumed as oral contraceptives, menopausal hormone therapy and treating infertility, resulting into the deleterious effects due to its endocrine disrupting activity. Furthermore, its presence as a potent endocrine disruptor in surface or environmental waters and various daily use products is another concern. Therefore, monitoring progesterone hormone is vital in environmental samples because of the adverse effects on reproductive health and causing hormonal imbalance. Herein, we have developed optical photoluminescence (PL) method implementing carbon dots (CDs) and graphene oxide (GO) based fluorescence resonance energy transfer (FRET) mechanism for progesterone hormone sensing. In this method, firstly progesterone-specific antibodies are covalently functionalized to CDs whose fluorescence has been quenched (turn off) by adding GO. However, the presence of progesterone increases the distance between donor and acceptor moieties and turns-on the fluorescence by displacing GO off the surface of CDs which in turn substantially reduces the FRET efficiency. Various optimization steps have been performed under control experiments to tune the fluorescence of CDs and the concentration of graphene oxide for maximum efficiency. In conclusion, a linear relationship is achieved in between PL intensity and different progesterone concentrations (10-900 nM) with 13.8 nM detection limits (R2=0.974). The structural and morphological analysis (XPS, and FT-IR) revealed the structural and surface functionalities of CDs. Finally, the potential of the developed biosensor has been explored in water matrices.

Efficient FRET process between CsPbBr3 quantum dots and RhB dye molecules by pressure regulation

Fluorescence resonance energy transfer (FRET) based on quantum dots (QDs) and dye molecules have great application potential in biochemical fields. How to achieve an efficient energy transfer process has become an important research topic. Pressure can be used to regulate the energy transfer process, but its regulation on metal halide perovskite systems is rarely reported. Herein, the efficient FRET process between CsPbBr3 QDs and Rhodamine B (RhB) molecules under high pressure is investigated. Upon compression to 1.3 GPa, the FRET rate of the CsPbBr3–RhB composite reaches 0.21 ns−1 and the FRET efficiency is improved from 12.4% to 62.4%, due to enhanced spectral overlap and shortened minimum distance between CsPbBr3 QDs and RhB molecules. This study provides a strategy for achieving efficient FRET research and further promotes the development of applications based on halide perovskite molecular systems.

Plasmon‐enhanced FRET biosensor based on Tm3+/Er3+ co‐doped core‐shell upconversion nanoparticles for ultrasensitive virus detection

AbstractOutbreaks of infectious viruses offer a formidable challenge to public healthcare systems and early detection of viruses is essential for preventing virus propagation. In this work, an ultrasensitive plasmon‐enhanced fluorescence resonance energy transfer (FRET) biosensor based on core‐shell upconversion nanoparticle (csUCNP) and gold nanoparticle (AuNP) for accurate detection of SARS‐CoV‐2 viral RNA is presented. In this biodetection assay, the Tm3+/Er3+ co‐doped csUCNP NaGdF4:Yb/Tm@NaYF4:Yb/Er acts as an energy donor and AuNP serves as an energy acceptor. The upconversion emission of Tm3+ and the design of the core‐shell structure led to a simultaneous surface plasmon effect of AuNP. The localized surface plasmon resonance (LSPR) arising from collective oscillations of free electrons significantly enhanced FRET efficiency between Er3+ and AuNP. The as‐prepared biosensor obtained a limit of detection (LOD) as low as 750 am, indicating that the integration of FRET and surface plasmon into one biodetection assay significantly boosted the sensitivity of the biosensor. In addition, samples extracted from clinical samples are also utilized to validate the effectiveness of the biosensor. Therefore, this innovative plasmon‐enhanced FRET biosensor based on Tm3+/Er3+ co‐doped csUCNP may pave the way for rapid and accurate biodetection applications.

Attomolar-level detection of respiratory virus long-chain oligonucleotides based on FRET biosensor with upconversion nanoparticles and Au–Au dimer

Upconversion nanoparticles (UCNPs) are promising nanoprobes in DNA/RNA detection, such as respiratory viral RNAs, and siRNA in cancer. However, recent studies have indicated that the sensitivity of UCNP-based biosensors is restricted, ranging from picomolar to femtomolar level. Moreover, most of existing UCNP-based probes are only able to detect short-chain oligonucleotides, which are not suitable for detection of long-chain oligonucleotides in many real applications. In this work, we introduced a new UCNP-based fluorescence resonance energy transfer (FRET) nanoprobe design composed of NaGdF4:Yb3+, Er3+@NaGdF4 core-shell UCNPs (csUCNPs) linking with Au–Au dimer to detect long-chain oligonucleotides of SARS-CoV-2 N-gene. Compared with typical single gold nanoparticles (AuNPs) in FRET biosensors, our theoretical investigation shows that a stronger electromagnetic field is generated in the Au–Au dimer where the plasmon resonance can enhance FRET efficiency and increase the working distance. Thus, the synergetic effect of plasmonic resonance and FRET enables a greater quenching efficiency (QE) of Au–Au dimer to UCNPs, which leads to more remarkable upconversion luminescence (UCL) recovery for each target gene recognition. Importantly, our design significantly improved the limit of detection (LOD) to attomolar level, with a linear response ranging from 2 aM to 2 fM. Moreover, the clinical detection with inactivated SARS-CoV-2 samples was successfully performed with excellent specificity within 30 min using the developed UCNPs biosensors incorporated with Au–Au dimer. This UCNP biosensor based on Au–Au dimer strategy with ultra-sensitivity and good selectivity opens a new path for clinical diagnosis without target amplification and plays an instructive role in other virus diagnosis.

Color‐Tunable Carbon Dots with Aggregation‐Induced Emission Constructed by FRET between Surface Luminescence Centers

AbstractAs a class of new fluorescent materials, carbon dots (CDs) have drawn widespread attention by virtue of their tunable photoluminescence (PL), excellent biocompatibility, and novel physicochemical properties. Unfortunately, in solid state, most CDs experience serious aggregation‐caused quenching (ACQ). In this work, color‐tunable CDs with aggregation‐induced emission (AIE) are prepared by simply changing the filling ratio of the autoclave. The obtained CDs show dual emission (green/red) in solid state, and the fluorescent color can be tuned from green to red. These CDs all exhibit blue fluorescence in dilute solution, and aggregation‐induced redshift behaviors are observed when the CDs form aggregates. Structural and optical characterizations prove that blue fluorescence is contributed by the carbon cores, whereas the green/red emission is attributed to the surface groups. Multicolor fluorescence is caused by increased fluorescence resonance energy transfer (FRET) efficiency among the dual emission (green/red) peaks from g‐CDs to r‐CDs. Surprisingly, delayed fluorescence (DF) of CDs are brightened by inserting the CDs into poly(vinyl alcohol) (PVA) films, which can be easily recognized by the naked eyes with a lifetime up to ms. Finally, owing to the unique AIE and DF properties, the four CDs can be applied to multimodal advanced anti‐counterfeiting and information encryption.

Heterodimerization of Human UDP-Glucuronosyltransferase 1A9 and UDP-Glucuronosyltransferase 2B7 Alters Their Glucuronidation Activities.

Human UDP-glucuronosyltransferases (UGTs) play a pivotal role as prominent phase II metabolic enzymes, mediating the glucuronidation of both endobiotics and xenobiotics. Dimerization greatly modulates the enzymatic activities of UGTs. In this study, we examined the influence of three mutations (H35A, H268Y, and N68A/N315A) and four truncations (signal peptide, single transmembrane helix, cytosolic tail, and di-lysine motif) in UGT2B7 on its heterodimerization with wild-type UGT1A9, using a Bac-to-Bac expression system. We employed quantitative fluorescence resonance energy transfer (FRET) techniques and co-immunoprecipitation assays to evaluate the formation of heterodimers between UGT1A9 and UGT2B7 allozymes. Furthermore, we evaluated the glucuronidation activities of the heterodimers using zidovudine and propofol as substrates for UGT2B7 and UGT1A9, respectively. Our findings revealed that the histidine residue at codon 35 was involved in the dimeric interaction, as evidenced by the FRET efficiencies and catalytic activities. Interestingly, the signal peptide and single transmembrane helix domain of UGT2B7 had no impact on the protein-protein interaction. These results provide valuable insights for a comprehensive understanding of UGT1A9/UGT2B7 heterodimer formation and its association with glucuronidation activity. SIGNIFICANCE STATEMENT: Our findings revealed that the H35A mutation in UGT2B7 affected the affinity of protein-protein interaction, leading to discernable variations in fluorescence resonance energy transfer efficiencies and catalytic activity. Furthermore, the signal peptide and single transmembrane helix domain of UGT2B7 did not influence heterodimer formation. These results provide valuable insights into the combined effects of polymorphisms and protein-protein interactions on the catalytic activity of UGT1A9 and UGT2B7, enhancing our understanding of UGT dimerization and its impact on metabolite formation.

Synthesis, photophysical, and photochemical properties of functional molecules based on a novel zinc(II) phthalocyanine-1,8-naphthalimide skeleton

Designing multifunctional photosensitizers with high efficiency has been significant in the molecular engineering field. In this work, we designed a novel molecular skeleton with a bi-chromophore, in which four 4-substituted-1,8-naphthalimide fluorophores were introduced as energy pumps to the zinc(II) phthalocyanine photosensitive group. Four peripherally symmetrical 4-NH-substituted-1,8-naphthalimide functionalized zinc(II) phthalocyanine molecules (NAZP1, NAZP2, NAZP3, NAZP4) were synthesized and characterized. The photophysical and photochemical properties of the molecules were investigated. The novel molecules showed dual-channel absorption and emission features of both chromophores. The fluorescence resonance energy transfer (FRET) process from 1,8-naphthalimide to zinc(II) phthalocyanine was verified by the spectral overlap and theoretical calculations. NAZP1 had higher FRET efficiency than the other three molecules. The singlet oxygen quantum yields of NAZP1, NAZP2, NAZP3, and NAZP4 in DMF were 0.84, 0.60, 0.68, and 0.73 respectively, being higher than the unsubstituted ZnPc. The introduction of four 1,8-naphthalimide energy pumps greatly improved the photophysical and photochemical properties of zinc(II) phthalocyanine, being hopeful in developing high-performance photosensitizers.

Engineering highly efficient NIR-II FRET platform for Background-Free homogeneous detection of SARS-CoV-2 neutralizing antibodies in whole blood

Förster or fluorescence resonance energy transfer (FRET) enables to probe biomolecular interactions, thus playing a vital role in bioassays. However, conventional FRET platforms suffer from limited sensitivity due to the low FRET efficiency and poor anti-interference of existing FRET pairs. Here we report a NIR-II (1000–1700 nm) FRET platform with extremely high FRET efficiency and exceptional anti-interference capability. This NIR-II FRET platform is established based on a pair of lanthanides downshifting nanoparticles (DSNPs) by employing Nd3+ doped DSNPs as an energy donor and Yb3+ doped DSNPs as an energy acceptor. The maximum FRET efficiency of this well-engineered NIR-II FRET platform reaches up to 92.2%, which is much higher than most commonly used ones. Owing to the all-NIR advantage (λex = 808 nm, λem = 1064 nm), this highly efficient NIR-II FRET platform exhibits extraordinary anti-interference in whole blood, and thus enabling background-free homogeneous detection of SARS-CoV-2 neutralizing antibodies in clinical whole blood sample with high sensitivity (limit of detection = 0.5 μg/mL) and specificity. This work opens up new opportunities for realizing highly sensitive detection of various biomarkers in biological samples with severe background interference.

A comparative study of conventional FRET and light harvesting properties of Rh-110/Rh-6G and Rh-19/Rh-B organic dye pairs impregnated in sol-gel glasses

Two different pairs of laser dyes, Rhodamine-110 (Rh-110)/Rhodamine-6G (Rh-6G) and Rhodamine-19 (Rh-19)/Rhodamine-B (Rh-B) (the first dye in each pair as a donor and the second as an acceptor) were impregnated in silica samples prepared by the sol-gel method and spectroscopically studied using absorption and steady-state fluorescence techniques. The critical transfer distance (R0), actual distance (r) between the donor and acceptor, overlap integral [J()], FRET (fluorescence resonance energy transfer) efficiency (E), and antenna effect efficiency (AE) were investigated in detail based on the variation in acceptor concentration. The FRET efficiency, antenna effect efficiency, and actual donor-acceptor distance for Rh-110/Rh-6G and Rh-19/Rh-B dye pairs corresponding to acceptor concentration ranges (3.83 to 7.65) × 10−5 M l−1 and (3.71 to 8.34) × 10−5 M l−1, respectively, were found to be in the ranges of 57.38% to 74.89%, 36.97% to 24.13%, 5.44 nm to 4.77 nm, and 77.01%. Furthermore, maximum FRET efficiencies of 85.68% and 87.63% and antenna effect efficiencies of 36.97% and 40.95% for Rh-110/Rh-6G and Rh-19/Rh-B, respectively, were also reported. Our results demonstrate the superior FRET efficiency of Rh-19/Rh-B over Rh-110/Rh-6G dye pair in sol-gel glasses, while the antenna effect efficiency of Rh-110/Rh-6G is higher than that of Rh-19/Rh-B for the same donor to acceptor (D/A) ratio. Finally, Rh-110/Rh-6G is a better energy harvester than the Rh-19/Rh-B dye pair at the common D/A ratio. These results are explained in terms of molecular structure similarity, polarity, and rigidity of donor and acceptor.

A novel acetylcholinesterase regulated upconversion-FITC fluorescence aptasensor for supersensitive detection of sulfadiazine in aquatic products

In this study, a novel fluorescence aptasensor was designed for the detection of sulfadiazine (SDZ) based on the pH-sensitive strategy to improve the fluorescence resonance energy transfer (FRET) efficiency. Acetylcholinesterase (AChE) was employed to regulated microenvironment responsiveness of the FRET between upconversion nanoparticles (UCNPs) as donors and pH-sensitive fluorescein isothiocyanate (FITC) dye as the effective acceptor. An energy transfer effect resulted in FITC strongly quenched the fluorescence of UCNPs. Upon addition of acetylthiocholine (ACh) and cDNA-modified AChE (cDNA-AChE), cDNA-AChE was assembled with aptamer functionalized FITC-modified UCNPs (UCNPs-FITC-aptamer), and the product of catalytic hydrolysis (acetic acid) changed the pH of the microenvironment surrounding UCNPs, causing the quenched fluorescence restored. The specific recognition of aptamer to SDZ broke the assembly composition, and reduced the recovery of fluorescence response signal. The linear relationship was achieved over the concentration range from 0.1 to 100 ng/mL and the limit of detection (LOD) was 0.031 ng/mL. In addition, the developed biosensor exhibited satisfactory results with (p > 0.05) enzyme-linked immunosorbent assay (ELISA). The excellent performance of the proposed biosensor confirmed the enormous potential to detect SDZ residuals in aquatic products.

Energy Funneling from Water-Dispersed Perovskites to Chromophores

Cesium lead halide perovskite nanocrystals (PNCs) have enjoyed enormous attention in optoelectronics and photovoltaics. However, instability under polar conditions and limited energy/charge transport due to long-chain capping ligands restrict their large-scale applications. We have engineered a short-chain multidentate bolaamphiphilic ligand (NKE-3), which provides synergistic passivation of the perovskite surface by one multidentate ionic terminal and localizes water molecules by another multidentate ionic terminal, leading to a water-suspended colloidal solution of PNCs. NKE-3 allows efficient long-range dipole-based fluorescence resonance energy transfer (FRET) from perovskites to Rhodamine B isothiocyanate (RITC) in water, with FRET efficiencies ranging from 96% to 98%. We calculated the FRET rate using the acceptor’s rise-time component, as it ensures no contamination from FRET-inactive donors. Moreover, we tuned the emission maxima of PNCs through halide exchange to optimize FRET efficiency. Such energy funneling to a suitable molecular photocatalyst is imperative for PNCs’ potential applications.

Fluorescence lifetime analysis of smFRET with contribution of PIFE on donor and acceptor.

Single-molecule fluorescence resonance energy transfer (FRET) is a powerful technique based on dipole-dipole interaction between donor and acceptor fluorophores to observe inter- and intra-molecular dynamics in real time with sensitivity to macro-molecular distances (∼2.5-10 nm). That said, some fluorophores have an inherent characteristic known as protein induced fluorescence enhancement (PIFE). PIFE is a photo-physical feature of dyes undergoing cis-trans transitions and occurs for protein-dye interactions closer than 3 nm where FRET is less sensitive. Here, the challenge is uncoupling the PIFE effect in the FRET data. Ignoring the PIFE effect in the analysis of the FRET data may lead to misinterpretation of the system under investigation. As a solution to this problem, we develop a computational framework based on Bayesian statistics to analyze the fluorescence lifetime signals of the donor and acceptor channels which allows us to uncouple the PIFE effects from the FRET. Our framework can extract any changes in the FRET efficiency simultaneously with any changes in the fluorescence lifetimes of the donor and acceptor due to the PIFE effect. In addition, our framework can provide other parameters, such as the donor and acceptor excitation rates, background photon rates, and detectors’ cross-talk ratios. Our framework extracts all these parameters by analyzing a single photon arrival time trace with only a few thousand photons.

Interaction of Ibuprofen with Partially Unfolded Bovine Serum Albumin in the Presence of Ionic Micelles and Oligosaccharides at Different λex and pH: A Spectroscopic Analysis.

The interaction between the plasma protein bovine serum albumin (BSA) and the drug ibuprofen (IBU) has been investigated at three different pH values (7.4, 6.5, and 8.0) in the presence of oligosaccharides and surfactants. The interaction analysis of BSA with oligosaccharides and surfactants has also been studied in the absence of the drug ibuprofen. The results obtained give convenient and efficient access to understand the mechanism of binding of ibuprofen to BSA, and the major forces involved are found to be hydrophobic forces, hydrogen bonding and ionic interactions. In addition to that, the formation of inclusion complexes of ibuprofen with oligosaccharides (β-CD and 2-HP-β-CD) has been observed, which has depicted that due to the hydrophobic nature of ibuprofen, it becomes more soluble in the presence of oligosaccharides, but due to the larger size of the inclusion complexes, these could not be able to access the hydrophobic pocket of BSA where tryptophan-212 (Trp-212) resides. The binding interaction between BSA and ibuprofen is observed in the presence of surfactants (SDS and CTAB), which partially unfold the protein. Non-radiative fluorescence resonance energy transfer (FRET) from Trp and Tyr residues of BSA in the presence of an anionic surfactant SDS to ibuprofen has depicted that there is a possibility of drug binding even in the partially unfolded state of BSA protein. Furthermore, the distance between the protein and the drug has been calculated from the FRET efficiency, which gives a comprehensive overview of ibuprofen binding to BSA even in its partially denatured state. The hydrophobic drug binding to the partially unfolded serum albumin protein (BSA) supports the "necklace and bead structures" model and opens up a new direction of drug loading and delivery system, which will have critical therapeutic applications in the efficient delivery of pharmacologically prominent drugs.

Fluorogenic response from DNA templated micrometer range self-assembled gold nanorod.

Plasmonic gold nanorod (AuNR) on a macromolecular matrix exhibits an end-to-end (ETE) long-range self-assembly (AuNR)n with n > 100. In the case of small molecules as a template, the pre-synthesized macromolecular matrix is missing and this brings a synthetic challenge in directed long-range assembly of AuNR. Self-assembly with thiol-modified small DNA and AuNR shows a much short-range ETE assembly with n < 25 via a simple evaporation technique on a solid surface. In this study, the introduction of two short amine modified probe DNAs (∼2.5 nm) and one 22-mer complementary single strand (ss)-DNA template (∼7 nm) show the long-range ETE self-assembly of (AuNR)n with n > 130. In the solution state, the zigzag arrangement within the assembled structure controls the typical change in the absorption behavior for (AuNR)n ETE assembly. The formation of this long-range ETE self-assembly in a solution state was verified from the combined effect of fluorescence resonance energy transfer (FRET) and hotspot-induced fluorescence enhancement. The probe DNAs and templated DNA concentration on fluorescence enhancement have been varied to monitor the effect of (AuNR)n with n = ∼5-130 in ETE self-assembly. Primarily quenched FRET acceptor in the presence of AuNR decisively exhibits remarkable fluorogenic response in ETE self-assembly with maximum n value. Although the FRET efficiencies among the fluorophores are comparable, the fluorogenic boost in ETE AuNR is due to the increased number of intrinsic navigated hotspots in these assemblies.

Visualizing Neurons Under Tension In Vivo with Optogenetic Molecular Force Sensors.

The visualization of mechanical stress distribution in specific molecular networks within a living and physiologically active cell or animal remains a formidable challenge in mechanobiology. The advent of fluorescence-resonance energy transfer (FRET)-based molecular tension sensors overcame a significant hurdle that now enables us to address previously technically limited questions. Here, we describe a method that uses genetically encoded FRET tension sensors to visualize the mechanics of cytoskeletal networks in neurons of living animals with sensitized emission FRET and confocal scanning light microscopy. This method uses noninvasive immobilization of living animals to image neuronal β-spectrin cytoskeleton at the diffraction limit, and leverages multiple imaging controls to verify and underline the quality of the measurements. In combination with a semiautomated machine-vision algorithm to identify and trace individual neurites, our analysis performs simultaneous calculation of FRET efficiencies and visualizes statistical uncertainty on a pixel by pixel basis. Our approach is not limited to genetically encoded spectrin tension sensors, but can also be used for any kind of ratiometric imaging in neuronal cells both in vivo and in vitro.