Twisted intramolecular charge transfer (TICT) based fluorescent probe for lighting up serum albumin with high sensitivity in physiological conditions

A microenvironment-sensitive red emissive probe with a large Stokes shift for specific recognition and quantification of serum albumin in complex biofluids and live cells

Human serum albumin (HSA) is regarded as a useful biomarker for rapid medical diagnosis of various disorders mainly related to the kidneys and liver. Hence, it is crucial to identify and monitor the HSA level in complex biofluids (urine and blood samples) using a simple approach. Herein, we have designed and synthesized an intramolecular charge transfer (ICT) based environment-sensitive fluorescent molecular probe, (E)-2-(3-(2-(5-methoxy-1H-indol-3-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (DCI-MIN), that can selectively interact with HSA in PBS buffer solution and exhibit a ∼78-fold enhancement in fluorescence intensity with a significant Stokes shift (∼126 nm), which is important to avoid interference from the excitation light. The significant red fluorescence response can be attributed to the suppression of free intramolecular rotation of the DCI-MIN probe inside the hydrophobic binding cavity of HSA and the low polar microenvironment present within HSA. According to the 3σ/slope method, the detection limit was found to be 1.01 nM (0.0671 mg L-1) in aqueous solutions, which is significantly lower than the normal level of HSA in healthy urine and blood serum, indicating its high sensitivity. DCI-MIN has the ability to exhibit useful applications, including the detection and quantification of HSA concentration in complex biofluids (human urine and blood samples) as well as the imaging of serum albumin in living cells.

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.

A Label-Free Optical Biosensor Based on an Array of Microring Resonators for the Detection of Human Serum Albumin

We introduced a label-free sensing system based on an array of microring resonators (MRRs) which was successfully employed for human serum albumin (HSA) detection. The sensing-ring surface was functionalized to immobilize anti-HSA, facilitating HSA binding. Our refractive index sensing system demonstrates high sensitivity at 168 nm/RIU and a low limit of detection (LOD) of 63.54 ng/mL, closely comparable to current HSA detection methods. These findings confirm the potential of MRRs as biocompatible sensors for HSA detection. This system holds great promise as an innovative platform for the detection of HSA, carrying significant importance in medical diagnostics.

Detection of human serum albumin using a rare-earth nanosheet fluorescent probe based on intensity and lifetime signals

Human serum albumin (HSA) is an important biomarker for early disease diagnosis. Therefore, the detection of HSA in biological samples is important. In this study, for the sensitive detection of HSA, a fluorescent probe based on Eu(III)-doped yttrium hydroxide nanosheets was designed and sensitized by α-thiophenformyl acetone trifluoride as an antenna. The morphology and structure of the as-prepared nanosheet fluorescent probe were studied by transmission electron microscopy and atomic force microscopy. A detailed investigation of the fluorescence properties of the as-obtained nanosheet probe revealed that the Eu(III) emission intensity was linearly and selectively enhanced by the consecutive addition of HSA. Furthermore, the lifetime signal of this probe was enhanced with increasing concentration. The sensitivity of the nanosheet probe to HSA is discussed based on the results of ultraviolet-visible, fluorescence, and infrared spectral analyses, the findings demonstrate that the nanosheet fluorescent probe we prepared is a highly sensitive and selective tool for detecting HSA concentration with a high intensity and a large lifetime change.

A novel fluorescence probe for the detection of water content in organic solvents and the distinction between deuterated and nondeuterated reagents

A novel D-π-A type fluorescent probe (probe 1) was developed for water content detection in organic solvents. By analyzing the relationship between fluorescence and water content, the probe was successfully applied to determine trace water content in tetrahydrofuran, ethyl acetate, 2-butanone, acetone, dimethylformamide, and acetonitrile. High water content in THF and ethyl acetate was associated with a gradual colour change from yellowish green to earthy yellow. The red/green value had a linear relationship with the water content in THF and ethyl acetate. There was a linear relationship between the red/blue value and water content in 2-butanone and acetone. Furthermore, probe 1 could be used for human serum albumin detection. Unexpectedly, probe 1 had a different colour response in deuterated and nondeuterated solvents, and had different fluorescence intensity and fluorescence emission wavelength. Probe 1 is rare tool that can distinguish between deuterated and nondeuterated reagents.

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.

Synthesis of a new environment-sensitive fluorescent probe based on TICT and application for detection of human serum albumin and specific lipid droplets imaging

Environment-sensitive fluorescent probes have always been as forceful tools to understand the pathophysiological processes of relevant diseases. In this work, a new fluorescent probe with typical D-π-A structure was designed and showed high sensitivity to polarity and viscosity changes. DPAR could selectively detect human serum albumin (HSA) with turn-on orange emission in aqueous PBS buffer (pH 7.4), which showed advantages such as rapid response (4 min), high sensitivity (LOD 0.98 μg/mL). Therefore, it was successfully used for achieving HSA levels in urine samples and HSA imaging in HeLa cells. DPAR also exhibited the capability to recognize the cancer cells over the normal cells by lower polarity guided lipid droplets (LDs) imaging (in green emission channel). The detection mechanism for HSA and cancer diagnosis was convinced that DPAR encountered the lower-polarity and higher-viscosity microenvironment, resulting in the confinement of the TICT process and intramolecular rotation. These facts showed that DPAR had good application prospects in environment-related biomedical research and clinical diagnosis.

Dysregulated Arginine Metabolism in Young Patients with Chronic Persistent Asthma and in Human Bronchial Epithelial Cells

Background: Recent metabolomics studies have found circulatory metabolism alterations in patients with asthma, indicating that altered metabolites played a significant role in asthma. However, the regulatory mechanisms in asthma, especially in young chronic persistent asthma remain underexplored. Methods: In this study, a prospective cohort of 162 patients diagnosed of asthma admitted to the First Affiliated Hospital of Xi’an Jiaotong University from January 2018 to December 2019 was used to perform a nested case-control study. Among them, we included 30 patients with chronic persistent asthma between 20 to 35 years old; 30 health control with evenly distributed age and sex were then recruited. Nontargeted metabolomics was applied to identify serum metabolic profiles and altered metabolic pathways. Results: In vitro, human bronchial epithelial cells (HBECs) line BEAS-2B with the addition of L-citrulline and/or asymmetric dimethylarginine (ADMA) model was utilized and the concentrations of nitric oxide (NO) metabolites were tested to evaluate the therapeutic potential of L-citrulline. The young patients with chronic persistent asthma displayed dysregulated serum metabolic profiles, especially enriched in arginine metabolism. The ratio of L-citrulline to ornithine is associated with blood eosinophil count. In vitro, adding L-citrulline could reverse ADMA-mediated reduction of NOx at lower L-arginine concentration (25 μM), but was ineffective in the higher L-arginine concentration (100 μM) media. Conclusions: The arginine metabolism balance is of vital importance during the pathogenesis and progression of chronic asthma. L-citrulline could be a powerful approach to restore airway NO production, potentially exhibiting therapeutic benefits among young patients with chronic asthma.

A Novel D-A-D Photosensitizer for Efficient NIR Imaging and Photodynamic Therapy

Photodynamic therapy (PDT) has attracted great interest in cancer theranostics owing to its minimal invasiveness and low side effect. In PDT, photosensitizers are indispensable components that generate cytotoxic reactive oxygen species (ROS). Tremendous efforts have been devoted to optimizing the photosensitizer with enhanced ROS efficiency. However, to improve the precision and controllability for PDT, developing NIR imaging-guided photosensitizers are still urgent and challenging. Here, we have designed a novel photosensitizer 2Cz-BTZ which integrated with intense NIR emission and photoinduced singlet oxygen ¹ O₂ generation capabilities. Moreover, after loading the photosensitizers 2Cz-BTZ into biocompatible amphiphilic polymers F127, the formed 2Cz-BTZ@F127 nanoparticles (NPs) exhibited good photoinduced therapy as well as long-term in vivo imaging capabilities. Under these merits, the 2Cz-BTZ@F127 NPs showed NIR imaging-guided PDT, which paves a promising way for spatiotemporally precise tumor theranostics.

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.

Theoretical study on the sensing mechanism of a coumarin-based fluorescent probe for biological thiols

The sensing mechanism of a reported fluorescence probe for cysteine, homocysteine and glutathione (Yin et al., 2018) has been investigated by time-dependent density functional theory. Experimental absorption and emission spectra of the probe before and after thiol addition were reproduced well by theoretical calculations, which validated the rationality of the method. Optimized geometries showed that the probe molecule had distinctly different geometries in its ground and excited states. It corresponded to the photoisomerization process and explained the weak fluorescence of the probe molecule. Moreover, by the potential energy curve scan, photoisomerization was further confirmed to be a spontaneous process with a barrier that barely existed. Frontier orbital analysis indicated that this photoinduced isomerization of the probe molecule derived from the antibonding character for lowest unoccupied molecular orbital at its CC double bond. In contrast, probe-thiol complexes exhibited similar geometries in their ground and excited states, which was responsible for the strong fluorescence of the probe with thiols. Due to distinct excited-processes, the probe can be used to sense thiols by monitoring the fluorescent change.

Strategy for optical data encryption and decryption using a D-A type stimuli-responsive AIE material

In this study, we report a new donor-acceptor (D-A) type stimuli-responsive material, (E)-4-(((9-ethyl-9H-carbazol-2-yl)methylene)amino)benzoic acid (C1), which possesses both aggregation-induced emission (AIE) and intramolecular charge transfer (ICT) natures. It glows green photoluminescence which changes into yellow color in response to mechanical stimuli, and fumigation in volatile organic compounds (VOCs) can switch the emission back to the initial state with high reversibility. In addition, the C1 film glows yellow-orange light, but turns into blue emission under continuous fumigation in ethyl acetate vapor. However the vapochromism behaves different when the C1 film is smeared: The emission of the smeared film is similar to the unsmeared but changes into cyan color after fumigation. The differences in vapochromism between smeared and unsmeared film can be easily distinguished by naked eyes. As revealed by SEM, the as-prepared film undergoes a morphology change from ill-shaped particles to microspheres in response to organic vapor, while the smeared film with scratched surface changes into dendritic patterns. According to the morphology study, the vapochromic luminescence can be ascribed to the physical adsorption of ethyl acetate vapor and the resulting change in the ICT process. In light of the unique vapochromism of C1, a new encryption-decryption technique for data recording was developed. Information can be recorded on the C1 film by mechanical writing and simultaneously concealed. It can be only accessed via fumigation in organic vapor, demonstrating a reliable steganography technology.

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.

Deciphering the positional impact of chlorine in a new series of berberine analogues towards the superb-selective “turn-on” hydrophobic signaling of bovine serum albumin at physiological pH

We report a new 9-O-benzyl substituted berberine analogue for the selective detection of BSA with a limit of detection value of 3.30 nM.