A specific and biocompatible fluorescent sensor based on the hybrid of GFP chromophore and peptide for HSA detection

Asymmetric dumbbell dimers simultaneously supporting quasi-bound states in continuum and anapole modes for terahertz biosensing

Multi-resonant metasurfaces are of great significance in the applications of multi-band nanophotonics. Here, we propose a novel metasurface design scheme for simultaneously supporting quasi-bound states in continuum (QBIC) and other resonant modes, in which QBIC resonance is generated by mirror or rotational symmetry breaking in oligomers while other resonant modes can be simultaneously excited by rationally designing the shapes of meta-atoms within oligomers. As an example, the simultaneous excitation of QBIC and anapole modes are demonstrated in a dimer metasurface composed of asymmetric dumbbell-shaped apertures. Based on the far-field multipole decomposition and near-field electromagnetic field distributions, the origin mechanisms of QBIC and anapole mode are elucidated. The symmetry breaking of dumbbell-shaped dimer results in QBIC. Within a certain asymmetric variation range, the contributions of toroidal dipole moment and electric dipole moment with approximately equal magnitudes remain dominant, which allows the anapole mode to always present. The effectiveness of the proposed design scheme is further confirmed by the experimental results identical with the evolutions of numerical simulation. In terahertz biosensing experiments, the anapole mode exhibits a higher sensitivity of 271.3 GHz (nmol/μl)-1, whereas the QBIC can achieve a lower detection limit of 0.015 nmol/μl and expands the detection range by almost an order of magnitude. Our findings are beneficial to designing multi-resonant metasurfaces with different resonance modes and promote the corresponding applications in the fields of biosensing, lasers, filtering, and nonlinearity.

Molecularly imprinted electrochemiluminescence sensor based on a novel luminol derivative for detection of human serum albumin via click reaction

A novel luminol derivative of N-(1,4-dioxo-1,2,3,4-tetrahydrophthalazin-5-yl)acrylamide (DTA) with excellent luminescence efficiency was designed and synthesized. Furthermore, a molecularly imprinted electrochemiluminescence sensor (MIECLS) was fabricated to detect ultratrace levels of human serum albumin (HSA) with high sensitivity and selectivity via a click reaction. The molecularly imprinted polymers (MIPs) were formed on the electrode surface via electropolymerization with HSA as a template molecule and catechol as a monomer. In the detection process, the -SH group of HSA on the electrode and the C = C bond of acryloyl group in DTA formed a new C-S bond via the Michael addition reaction to construct the MIECLS. The higher the concentration of HSA, the greater electrochemiluminescence (ECL) intensity measured. Taking advantage of MIECLS for ECL detection (scanning potential, - 0.4 to 0.5 V), there was a good linear relationship between ECL intensity and the logarithm of HSA concentration in the range 5 × 10-9 to 1 × 10-13 mg mL-1. The limit of detection (LOD) of the sensor was 1.05 × 10-15 mg mL-1. The sensor exhibited outstanding selectivity and stability. The sensor was applied to detect HSA in human serum with good recoveries of 97.7-105.2%. The concentration of HSA was detected by electrochemical method using the gating effect of MIP.

Development of Human Serum Albumin Fluorescent Probes in Detection, Imaging, and Disease Therapy

Human serum albumin (HSA) acts as a repository and transporter of substances in the blood. An abnormal concentration may indicate the occurrence of liver- and kidney-related diseases, which has attracted people to investigate the precise quantification of HSA in body fluids. Fluorescent probes can combine with HSA covalently or noncovalently to quantify HSA in urine and plasma. Moreover, probes combined with HSA can improve its photophysical properties; probe-HSA has been applied in real-time monitoring and photothermal and photodynamic therapy in vivo. This Review will introduce fluorescent probes for quantitative HSA according to the three reaction mechanisms of spatial structure, enzymatic reaction, and self-assembly and systematically introduce the application of probes combined with HSA in disease imaging and phototherapy. It will help develop multifunctional applications for HSA probes and provide assistance in the early diagnosis and treatment of diseases.

Evaluation the binding of chlorogenic acid with bovine serum albumin: Spectroscopic methods, electrochemical and molecular docking

Chlorogenic acid(CGA) is the common active phenolic acid in Chinese medicinal materials such as honeysuckle and eucommia. It is a class of small molecules with multiple activities such as antioxidant, inhibiting cancer cells, lowering blood sugar and lowering blood pressure. In this paper, UV-vis spectroscopy, fluorescence spectroscopy, circular dichroism, molecular dynamics simulation and cyclic voltammetry (CV) electrochemical analysis were used to investigate the mechanism about interaction between CGA and BSA. Based on fluorescence quenching analysis, CGA quenched the inherent fluorescence of BSA remarkably through a static mechanism. The obtained value of binding constant (K_b = 5.75 × 10⁵ L·mol^-1) revealed a high binding affinity between CGA and BSA. The simulated molecular docking showed that hydrophobic force were also involved in the interaction between BSA and CGA. This paper also investigate the effect of temperature and metal ions on the binding of CGA and BSA. When the temperature increased, the binding of BSA and CGA was destroyed. Metal ions affect both the structure of BSA and the combination of BSA and CGA. By studying the mechanism of CGA interaction with BSA, we elucidated the storage and transport mechanism of CGA in vivo under simulated human environment and temperature conditions.

Nutritive Value of Active Volatile Components of Anacardiaceae Mango and Their Effects on Carrier Proteins Function

The effects of mango active volatile components (VOCs) on protein function were investigated from the perspective of nutrient transport. The active volatile components of five varieties of mango were analyzed by headspace solid phase microextraction gas chromatography-mass spectrometry (HS-SPME/GC-MS). The interaction mechanism between active volatile components and three carrier proteins was discussed by fluorescence spectroscopy, molecular docking and dynamic simulation. The results showed that there were 7 active components in the five mango varieties. The aroma components represented by 1-caryophyllene and β-pinene were selected for further study. The interaction between VOCs small molecules and proteins is a static binding process, and its main force is hydrophobic interaction. The results of molecular simulation and spectral experiments showed that the binding ability of 1-caryophyllene and β-pinene to β-Lg was strong, so mango VOCs could possess a certain nutritional value in dairy products, expanding its application in dairy products in the food industry.

A near-infrared dicyanoisophorone-based fluorescent probe for discriminating HSA from BSA

Despite the rapid development of fluorescent probe techniques for the detection of human serum albumin (HSA), a probe that discriminates between HSA and bovine serum albumin (BSA) is still a challenging task, since their similar chemical structures. As a continuation of our work, herein, a dicyanoisophorone-based fluorescent probe DCO2 is systematically studied for discrimination of HSA from BSA. The photophysical and sensing performances of DCO2, including basic spectroscopic properties, sensing sensitivity, and selectivity, exhibits that DCO2 could selectively bind with HSA and display remarkable fluorescence enhancement (∼254-fold) at 685 nm. The gap of the fluorescent response of DCO2 between HSA and BSA is an obvious increase from 21% to 73% compared to the previous probe DCO1. The sensing mechanism was elucidated by Job's plot, displacement experiment, and molecular docking, suggesting that the specific response to HSA originated from the rigid donor structure and steric hindrance. DCO2 could be buried in the DS1 pocket of HSA, and only partly wedged into the DS1 pocket of BSA with exposing twisted N,N-diethylamino group outside. Application studies indicated that DCO2 has well detective behavior for HSA in the biological fluids. This work could provide a new approach to design HSA-specific near-infrared fluorescence probes.

Modulating donor of dicyanoisophorone-based fluorophores to detect human serum albumin with NIR fluorescence

It is urgently needed to develop NIR-fluorescent probe for detection of human serum albumin (HSA) since the interference of short-wavelength-fluorescence from endogenous species in real serum and urine. However, most previous reports were located in the short-wavelength region (<600 nm). In this work, a series of dicyanoisophorone (DCO)-based fluorophores 1-4 with different donor groups have been designed and investigated. A systematic study of their photophysical properties has been carried out. Among these probes, 4 exhibited NIR emission with the highest fluorescence brightness and the most sensitive signal response to HSA. Further studies demonstrated that 4 could strongly bind into the DS1 pocket of HSA with a 1:1 ratio. Importantly, the method based on 4 has been proven to be capable of sensing HSA in real serum and urine samples.

A fluorescent sensor recognized by the FA1 site for highly sensitive detection of HSA

Human serum albumin (HSA), as the most abundant protein in blood plasma, plays a crucial role in many physiological processes. The abnormal HSA level in serum or in urine is often associated with various diseases. Therefore, to achieve highly sensitive and selective quantification of HSA is of great importance for disease diagnosis and preventive medicine. Herein, an HSA-selective light-up fluorescent sensor, DCM-ML, was successfully developed for quantitative detection of HSA. DCM-ML exhibited good (photo-) stability and strong fluorescence enhancement around 630 nm in the presence of HSA in complex samples containing numerous biological analytes. Upon addition of HSA into DCM-ML containing solution, a good linear relationship (R² > 0.99) between the fluorescence intensity of DCM-ML and HSA concentration from 0 to 0.08 mg/mL was obtained with the detection limit of 0.25 μg/mL. The sensing mechanism of the sensor towards HSA was demonstrated to be via recognition in the fatty acid site 1 (FA1), instead of the most reported binding sites (Sudlow I and II) in HSA, for the first time, by both the displacement experiments and molecular docking simulation. Thus, DCM-ML can also be assumed as a potential FA1 site-binding marker for examining drugs binding to the FA1 site in HSA. At last, the utilization of sensor DCM-ML for quantification and validation of HSA in urine samples and cell culture medium was effectively demonstrated. Therefore, the development of DCM-ML should find great application potentials in the fields of analytical chemistry and clinical medicine as a highly sensitive HSA sensor.

Highly selective fluorescent peptide-based chemosensors for aluminium ions in aqueous solution

Two novel fluorescent peptide-based chemosensors, including A (2-amino-benzoyl-Ser-Glu-Glu-NH₂) and B (2-amino-benzoyl-Ala-Glu-Pro-Glu-Ala-Glu-Pro-NH₂) were synthesized and characterized by nuclear magnetic resonance (NMR) spectra. These fluorescent probes exhibited excellent selective and sensitive responses to Al³⁺ ions over other metal ions in aqueous buffered solutions. The limits of detection for both chemosensors towards the Al³⁺ ions were in the order of ∼10^-7 M (A: 155 nM and B: 195 nM), which clearly indicates that these probes have significant potential for biological applications. They also displayed high binding affinity (1.3029 × 10⁴ M^-1 and 1.7586 × 10⁴ M^-1 relevant to A and B respectively). These two chemosensors are great analytical probes that produce turn-on responses upon binding to Al³⁺ ions through an intramolecular charge transfer (ICT) mechanism. In addition, the application of both chemosensors was examined over a wide range of pH. The fluorescent peptide-based probes and Al³⁺ form a 1:1 coordination complex according to the ESI-MS and Job's plot analysis. Notably, upon addition of Al³⁺ to these chemosensors, a fluorescence enhancement of approximately 8-fold was observed and the binding mode was determined using NMR titration and fluorescence emission data.

A red emitting fluorescent probe based on TICT for selective detection and imaging of HSA

A red emitting fluorescence probe, TPA-CPO, based on twisted intra-molecular charge transfer (TICT) was designed and synthesized. The spectra results displayed that TPA-CPO could sense HSA with excellent properties including significant fluorescence enhancement, long emission wavelength, large stokes shift, and wide linear range. The recognition mechanism was proved that TPA-CPO could bind to domain IB of HSA and its TICT process was suppressed by utilizing hydrophobic cavity and low polarity of HSA. TPA-CPO bind to domain IB instead of common drug sites of HSA could effectively avoid interference from most drugs. The selective response of TPA-CPO allowed quantitative detection of HSA with sensitivity limit of 13.65 µg/mL. What's more, it successfully achieved HSA imaging in HeLa cells.

A novel hydrazide Schiff base self-assembled nanoprobe for selective detection of human serum albumin and its applications in renal disease surveillance

Human serum albumin (HSA) is considered as a biomarker for the early diagnosis of renal disease, therefore identifying and detecting HSA in biological fluids (especially urine) with an easy method is of great importance. Herein, we report a novel hydrazide Schiff base fluorescent probe N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)pyrazine-2-carbohydrazide (NPC), which self-assembled into nanoparticles in aqueous solution. Based on disassembly-induced emission and the site-specific recognition mechanism, the binding of NPC with HSA resulted in a fluorescence "turn-on" response. Probe NPC exhibited superior selectivity and sensitivity toward HSA with a detection limit of 0.59 mg L-1 in PBS and 0.56 mg L-1 in the urine sample. The site-binding mechanism of NPC with HSA was explored by fluorescence quenching study, Job's plot analysis, HSA destruction, site marker displacement and molecular docking. Fluorescence imaging of HSA in MCF-7 cells was achieved by using a non-toxic NPC probe, suggesting that NPC could be applied to visualize the level of HSA in vivo. More importantly, further practical applications of probe NPC in human urine samples were achieved with satisfactory results by using a fluorometer or test paper, which could provide extensive application in clinical diagnosis.

Peptide-Engineered Fluorescent Nanomaterials: Structure Design, Function Tailoring, and Biomedical Applications

Fluorescent nanomaterials have exhibited promising applications in biomedical and tissue engineering fields. To improve the properties and expand bioapplications of fluorescent nanomaterials, various functionalization and biomodification strategies have been utilized to engineer the structure and function of fluorescent nanomaterials. Due to their high biocompatibility, satisfied bioactivity, unique biomimetic function, easy structural tailoring, and controlled self-assembly ability, supramolecular peptides are widely used as versatile modification agents and nanoscale building blocks for engineering fluorescent nanomaterials. In this work, recent advance in the synthesis, structure, function, and biomedical applications of peptide-engineered fluorescent nanomaterials is presented. Firstly, the types of different fluorescent nanomaterials are introduced. Then, potential strategies for the preparation of peptide-engineered fluorescent nanomaterials via templated synthesis, bioinspired conjugation, and peptide assembly-assisted synthesis are discussed. After that, the unique structure and functions through the peptide conjugation with fluorescent nanomaterials are demonstrated. Finally, the biomedical applications of peptide-engineered fluorescent nanomaterials in bioimaging, disease diagnostics and therapy, drug delivery, tissue engineering, antimicrobial test, and biosensing are presented and discussed in detail. It is helpful for readers to understand the peptide-based conjugation and bioinspired synthesis of fluorescent nanomaterials, and to design and synthesize novel hybrid bionanomaterials with special structures and improved functions for advanced applications.

Detection Methods and Research Progress of Human Serum Albumin

Human serum albumin (HSA) is a biological macromolecule with important physiological functions; abnormal HSA levels are associated with coronary heart disease, multiple myeloma, diabetes, nephropathy, neurometabolic disorders, liver cirrhosis and other diseases. Therefore, accurate and quantitative detection of HAS have extremely important research and application value in biological science, molecular biology, clinical medicine and other fields. As for the detection method of HSA, dye-binding method and immune method are the first to be used, and have been applied in clinical detection. In recent years, many new detection technologies have emerged, such as fluorescent probe detection method, nano-materials for HSA detection, biosensor and so on. Although there are many methods developed recently to detect HSA, comprehensive reviews for HSA detection methods are still rare. Thus, writing this review to fill in the blank is in need. In order to highlight the recent progress in the field of HSA detection, in this review, the methods used to detect HSA are summarized and sorted, the advantages and disadvantages of these detection methods are also listed, then the research progress of small molecular fluorescence probe method is emphatically introduced in this paper. Then, we briefly discussed the challenges and future development directions in this field.

Dual-Self-Restricted GFP Chromophore Analogues with Significantly Enhanced Emission

The tremendous gap of fluorescence emission of synthetic green fluorescent protein (GFP) chromophore to the protein itself makes it impossible to use for applications in molecular and cellular imaging. Here, we developed an efficient methodology to enhance the photoluminescence response of synthetic GFP chromophore analogues by constructing dual-self-restricted chromophores. Single self-restricted chromophores were first generated with 2,5-dimethoxy substitution on the aromatic ring, which were further modified with phenyl or 2,5-dimethoxy phenyl to form dual-self-restricted chromophores. These two chromophores showed an obvious solvatofluorochromic color palette across blue to yellow with a maximum emission Stokes shift of 95 nm and dramatically enhanced fluorescence emission in various aprotic solvents, especially in hexane, where the QY reached around 0.6. Importantly, in acetonitrile and dimethyl sulfoxide, the fluorescence QYs of both chromophores were over 0.22, which were the highest reported so far in high polar organic solvents. Meanwhile, the fluorescence lifetimes also improved obviously with the maximum of around 4.5 ns. Theoretical calculations revealed a more favorable Mülliken atomic charge translocation over the double-bond bridge and illustrated much higher energy barriers for the Z/E photoisomerization together with larger bond orders compared with the GFP core chromophore, p-HBDI. Our work significantly improved the fluorescence emission of synthetic GFP chromophore analogues in polar solvents while reserved the multicolor emitting function, providing a solid molecular motif for engineering high-performance fluorescent probes.

Spectroscopic Technique-Based Comparative Investigation on the Interaction of Theaflavins with Native and Glycated Human Serum Albumin

Theaflavin is a kind of multi-pharmacological and health beneficial black tea factor. The aim of this study is to investigate the mechanisms by which theaflavin interacts with glycosylated and non-glycosylated serum albumins and compares their binding properties. Fluorescence and ultraviolet spectra indicated that theaflavin interacted with native and glycated human serum albumin through a static quenching mechanism and had a higher degree of quenching of human serum albumin. The thermodynamic parameters revealed that the combinations of theaflavin with native and glycated human serum albumin were a spontaneous endothermic reaction, and the hydrophobic force was a major driving force in the interaction process. Zeta potential, particle size, synchronous fluorescence, three-dimensional fluorescence spectroscopy and circular dichroism further clarified the effect of theaflavin on the conformation of human serum albumin structure were more pronounced. In addition, site competition experiments and molecular docking technique confirmed that the binding sites of theaflavin on both native and glycated human serum albumin were bound at site II. This study had investigated the effects of glycation on the binding of HSA with polyphenols and the potential nutriology significance of these effects.

Synthesis and application of a water-soluble phosphorescent iridium complex as turn-on sensing material for human serum albumin

A novel water-soluble cyclometallated iridium complex [Ir(pq-COOH)₂FDS]^- (pq-COOH = 2-phenylquinoline-4-carboxylic acid, FDS = 3-(2-pyridyl)-5,6-bis(4-sulfophenyl)-1,2,4-triazine dianions) (abbreviated as Ir) was synthesized and its phosphorescent property was comprehensively studied. It was found that the complex exhibited strong phosphorescence, which peaked at 634 nm in neutral conditions (maximized at pH 8.0). Its phosphorescence decreased with an increase in acidity of the aqueous solution. At pH 2.0, the quenched phosphorescence could be resumed upon the addition of human serum albumin (HSA) because of the hydrophobic and electrostatic interactions between HSA and Ir. Based on this phenomenon, a "turn on" type phosphorescence probe was developed for the detection of HSA. Under optimal conditions, a wide calibration range of 1-280 nM was obtained with a limit of detection of 0.8 nM for HSA. The phosphorescence probe was successfully used for the determination of HSA in blood serum and urine samples.

A selective and sensitive fluorescent probe for the determination of HSA and trypsin

A simple fluorescent probe HBI-GR based on the combination of the fluorophore (p-HBI) in green fluorescent protein (GFP) and Guanine riboside (GR) for HSA was successfully synthesized. HBI-GR showed an obvious fluorescence enhancement toward HSA without interference from other proteins, amino acids, anions and commonly existing metal ions. HBI-GR exhibited high sensitivity towards HSA with a good linear relationship between the fluorescence intensity of HBI-GR and HSA concentration from 0 to 0.06mgmL^-1. The limit of detection, based on a signal-to-noise ratio of 3, was 15.09ngmL^-1, which was much lower than that of most other reported probes. HBI-GR was almost non-fluorescent because of the bond twisting in the exited state of chromophore HBI. After binding to the hydrophobic pocket of HSA, it showed an obvious fluorescence enhancement due to the rigidifying of the flexible chromophore HBI by the hydrophobic environment. The resulting HBI-GR/HSA system also showed a satisfactory sensing ability toward trypsin through decreased fluorescence intensity with the detection limit of 0.0282ngmL^-1. The fluorescence decreasing process was occurred as the lysine and arginine amino acids residues of HSA were cleaved by trypsin, which led to further exposure of HBI-GR to the PBS buffer phase and a concomitant decrease of the HBI-GR fluorescence intensity. Moreover, the probe HBI-GR was successfully used to detect HSA in healthy human urine and human blood serum samples. The practical application of the HBI-GR/HSA system for trypsin detection in healthy human urine also achieved satisfactory result.

Selectively switching on europium emission in drug site one of human serum albumin

A luminescent europium probe has been discovered that binds selectively to drug-site I in human serum albumin, signalled by a ‘switching on’ of europium emission, and accompanied by strong induced circularly polarised luminescence.