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

Advancements in molecular disassembly of optical probes: a paradigm shift in sensing, bioimaging, and therapeutics

The majority of self-assembled fluorescent dyes suffer from aggregation-caused quenching (ACQ), which detrimentally affects their diagnostic and therapeutic effectiveness. While aggregation-induced emission (AIE) active dyes offer a promising solution to overcome this limitation, they may face significant challenges as the intracellular environment often prevents aggregation, leading to disassembly and posing challenges for AIE fluorogens. Recent progress in signal amplification through the disassembly of ACQ dyes has opened new avenues for creating ultrasensitive optical sensors and enhancing phototherapeutic outcomes. These advances are well-aligned with cutting-edge technologies such as single-molecule microscopy and targeted molecular therapies. This work explores the concept of disaggregation-induced emission (DIE), showcasing the revolutionary capabilities of DIE-based dyes from their design to their application in sensing, bioimaging, disease monitoring, and treatment in both cellular and animal models. Our objective is to provide an in-depth comparison of aggregation versus disaggregation mechanisms, aiming to stimulate further advancements in the design and utilization of ACQ fluorescent dyes through DIE technology. This initiative is poised to catalyze scientific progress across a broad spectrum of disciplines.

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.

NIR-I emissive cyanine derived molecular probe for selective monitoring of hepatic albumin levels during hyperglycemia

In this study, we report a small molecule optical marker BI-CyG derived from the structural engineering of a cyanine scaffold. The developed probe offers suitable advantages over existing cyanine-based albumin specific probes in terms of its excitation and emission wavelengths, which are 760 and 830-832 nm, respectively. Structural tuning of the cyanine architecture leading to extended π-conjugation and resulting in a suitable bathochromic shift in the emission wavelength of the probe is represented in this study. The probe besides emitting in the NIR region, also possesses the desirable characteristics of being a potential target selective optical marker, as established from various biophysical studies. Molecular modelling and simulation studies provided critical insights into the binding of the probe in the protein microenvironment, which was further supported by experimental studies. The probe displayed intracellular albumin selectivity and was utilized for demonstrating alteration in albumin levels in pathological states such as hyperglycemia in hepatic cells. The present study also sheds some light on using BI-CyG as an imaging probe and on the role of metformin as a suitable drug for balancing hyperglycemia-induced reduced intra-hepatic albumin levels. The study, thus, attempts to highlight the structural derivatization of cyanine to afford a potential probe for serum albumin and its deployment to image altering albumin levels in an induced pathological condition, hyperglycemia.

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.

Development of a High-Accuracy, Low-Cost, and Portable Fluorometer with Smartphone Application for the Detection of Urinary Albumin towards the Early Screening of Chronic Kidney and Renal Diseases

This study presents the development of a portable fluorometer with a smartphone application designed to facilitate the early screening of chronic kidney and renal diseases by enabling the sensitive detection of urinary albumin. Utilizing a fluorescence-based aptasensor, the device achieved a linear calibration curve (0.001-1.5 mg/mL) with a linearity of up to 0.98022 and a detection limit of 0.203 µg/mL for human serum albumin (HSA). The analysis of 130 urine samples demonstrated comparable performance between this study's fluorometer, a commercial fluorometer, and the standard automated method. These findings validate the feasibility of the portable fluorometer and aptasensor combination as a reliable instrument for the sensitive and specific measurement of HSA in urine samples. Moreover, the fluorometer's portability offers potential applications in portable point-of-care testing, enhancing its utility in clinical settings for early disease screening.

Chiral 8-aminoBODIPY-based fluorescent probes with site selectivity for the quantitative detection of HSA in biological samples

Human serum albumin (HSA) is one of the vital proteins in blood serum, and its optimum level is a reflection of the physiological well-being of an individual. Any abnormalities in serum HSA levels could often be a sign of disguised physiological disorders. The importance of fast and accurate determination of serum HSA levels has led to the development of various quantification methods. Among these, fluorescence-based methods employ molecular probes capable of producing selective responses on interaction with HSA. Herein, we report chiral 8-aminoBODIPY-based probes having blue emission for the quantitative detection of HSA in buffer and human blood serum. A pair of 8-aminoBODIPY enantiomers, namely R-PEB and S-PEB, were synthesized. They exhibited a fast 'turn-on' fluorescence response towards HSA, allowing its detection and quantification. In PBS buffer, R-PEB and S-PEB showed very good sensitivity with a limit of detection (LoD) of 25 nM (K_D = 9.84 ± 0.14 μM) and 39 nM (K_D = 18.67 ± 0.21 μM), respectively. The linear relationship observed between the fluorescence intensity of R-PEB/S-PEB and the HSA concentration in serum samples allowed us to generate a reference curve for HSA estimation for practical applications. Examination of unknown serum samples showed a good correlation with the results obtained by the benchmark BCG method. Interestingly, the difference in these probes' dissociation constants and LoD indicated their differential binding to HSA. Considering the availability of multiple ligand binding sites in HSA, their binding preferences were investigated in detail by displacement assays using site-specific drugs. These studies showed the preferential affinity of R-PEB towards site II, which was further substantiated using molecular docking studies. However, these displacement assays could not identify the preferred binding site of S-PEB. Blind docking studies indicated that S-PEB occupied a site closer to FA5. Selective binding of R-PEB to site II and its characteristic photophysical response can be utilized to quickly screen potential site II binding drugs.

Serum Albumin Inspired Self-Assembly/Disassembly of a Fluorogenic Nanoprobe for Real-Time Monitoring and Quantification of Urinary Albumin with Live Cell Imaging Application

Abnormal levels (high/low) of urinary human serum albumin (HSA) are associated with a number of diseases and thus act as an essential biomarker for quick therapeutic monitoring and biomedical diagnosis, entailing the urgent development of an effective chemosensor to quantify the albumin levels. Herein, we have rationally designed and developed a small fluorogenic molecular probe, (Z)-2-(5-((8-hydroxy-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl) methylene)-4-oxo-2-thioxothiazolidin-3-yl) acetic acid (HJRA) with a twisted intramolecular charge transfer (TICT) property, which can easily self-assemble into nonfluorescent nanoaggregates in aqueous solution. However, HJRA nanoaggregates can selectively bind with serum albumin proteins (HSA/BSA) in ∼100% PBS medium, thereby facilitating the disassembly of nanoaggregates into monomers, exhibiting a clear turn-on red fluorescent response toward HSA and BSA. Analysis of the specific binding mechanism between HJRA and HSA using a site-selective fluorescence displacement assay and molecular docking simulations indicates that a variety of noncovalent interactions are responsible for the disassembly of nanoaggregates with the concomitant trapping of the HJRA monomer at site I in HSA, yielding a substantial red emission caused by the inhibition of intramolecular rotation of HJRA probe inside the hydrophobic cavity of HSA. The limit of detection (LOD) determined by the 3σ/slope method was found to be 1.13 nM, which is substantially below the normal HSA concentration level in healthy urine, signifying the very high sensitivity of the probe toward HSA. The comparable results and quick response toward quantification of HSA in urine by HJRA with respect to the Bradford method clearly point toward the superiority of this method compared to the existing ones and may lead to biomedical applications for HSA quantification in urine. It may also find potential application in live-cell imaging of HSA.

Dual-Channel Recognition of Human Serum Albumin and Glutathione by Fluorescent Probes with Site-Dependent Responsive Features

Design of chemical probes with high specificity and responses are particularly intriguing. In this work, a fluorescent probe (M-OH-SO₃) with dual-channel spectral responses toward human serum albumin (HSA) is presented. By employing dinitrobenzenesulfonate as a recognition site as well as a fluorescence quencher, probe M-OH-SO₃ displayed weak fluorescence, which, nevertheless, exhibits extensive yellow (575 nm) and red (660 nm) fluorescence emissions toward HSA under excitations at 400 and 500 nm, respectively. Interestingly, M-OH-SO₃ displayed the best performance toward HSA with distinctly higher selectivity than that of its counterparts M-SO₃, M-H-SO₃, and M-F-SO₃, which were prepared simply by modulating the functional group at the ortho position of the dicyanoisophorone core. Molecular docking results revealed that M-OH-SO₃ possesses the lowest binding energy among the tested derivatives and accordingly the strongest binding affinity. Probe M-OH-SO₃ showed a good linear relationship toward HSA in a range of 0.5-18 μM with a limit of detection of 35 nM. Cell imaging results demonstrated that probe M-OH-SO₃ could visualize the variation HSA levels in hepatocarcinoma cells. In addition, probe M-OH-SO₃ could also be employed for the recognition of glutathione through the cleavage of the dinitrobenzenesulfonate group along with an enhancement of emission at 575 nm. The site-dependent properties inspired a novel paradigm for design of fluorescent probes with optimized selectivity and responses.

Rationally designed far-red emitting styryl chromones and a magnetic nanoconjugate for strip-based 'on-site' detection of metabolic markers

The global burden of liver damage and renal failure necessitates technology-aided evolution towards point-of-care (POC) testing of metabolic markers. Hence in the prevalence of current health conditions, achieving on-site detection and quantifying serum albumin (SA) can contribute significantly to halting the increased mortality and morbidity rate. Herein, we have rationally designed and synthesized far-red emitting, solvatofluorochromic styryl chromone (SC) derivatives SC1 and SC2, and SC2-conjugated fluorescent magnetic nanoparticles (SCNPs) for sensing SA with a fluorogenic response via interacting at an atypical drug binding site. In solution, the highly sensitive and selective fluorogenic response was evaluated by the prominent amplification and blue-shift in the emission maxima of the probes from deep red to dark yellow through an intermediate orange emission. The transformation of the fluorogen into a fluorophore was manifested through spectroscopic measurements. The stabilization of the probes at protein pockets was ascribed to the non-covalent interactions, such as H-bonding, cation-π, and hydrophobic interactions, as unveiled by docking studies. The practical applications revealed the novelty of SC derivatives through (a) the capability to detect SA isolated from real blood samples via a turn-on fluorescence response; (b) the design of a simple, cheap, and portable test-strip using a glass-slide loaded with solid-state emissive SC2, which provided differential emission color of the SC2-HSA complex in solution and the solid-state with increasing concentration of HSA. Moreover, a smartphone-based color analysis application was employed to obtain the ratio of green and red (G/R) channels, which was utilized for quantitative detection of HSA; (c) the biocompatibility of the SC1 was ascertained through confocal laser scanning microscopic imaging (CLSM). Detailed investigation showed that SC1 could entirely localize in the mitochondria and evolve as a promising biomarker for distinguishing cancer cells from normal cells. Additionally, the validation of uncommon binding of SC1 and SC2 between domains I and III was determined using competition experiments with a known site-specific binder and molecular docking studies. This unique property of the probes can be further exploited to understand the cellular intake of HSA-drug complexes in the multifaceted biological system. These results find the utility of SC derivatives as small molecule-based chemosensors for at-home SA detection and as a biomarker for cancer.

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.

Near-infrared emissive cyanine probes for selective visualization of the physiological and pathophysiological modulation of albumin levels

With the promising advantages of the near-infrared region (NIR) emissive markers for serum albumin becoming very prominent recently, we devised CyG-NHS as the cyanine derived longest NIR-I emissive optical marker possessing albumin selective recognition ability in diverse biological milieu. Multiscale modeling involving molecular docking, molecular dynamics, and implicit solvent binding free energy calculations have been employed to gain insights into the unique binding ability of the developed probe at domain-I of albumin, in contrast to the good number of domain IIA or IIIA binding probes available in the literature reports. The binding free energy was found to be -31.8 kcal mol^-1 majorly predominated by hydrophobic interactions. Besides, the conformational dynamics of CyG-NHS in an aqueous medium and the albumin microenvironment have been comprehensively studied and discussed. The potentiality of this optical platform to monitor the intracellular albumin levels in human hepatoma (HepG2) cells in different pathophysiological states has been demonstrated here. Also, the competency of the phenformin drug in restoring the albumin levels in chronic hyperinsulinemic and hypercholesterolemic in vitro models has been established through the visualization approach. Altogether, the findings of this study throw light on the significance of the development of a suitable optical marker for the visualization of critical bioevents related to albumin.

Development of a human serum albumin structure-based fluorescent probe for bioimaging in living cells

Forming a stable complex is a prerequisite for intramolecular charge transfer (ICT) probe to recognize proteins. Herein, a human serum albumin (HSA) structure-based fluorescent probe DNPM was fabricated successfully with fully considering its binding to the primary sites in HSA. Molecular simulation was used to assist the probe design. Two ICT ligands DNPM and MPM were initially designed. Both DNPM and MPM had favorable HSA binding abilities, but only DNPM had a satisfactory HSA sensitivity. Electromagnetic coupling played a key role in DNPM fluorescence enhancement. Due to the electromagnetic environment difference in protein structure, DNPM only exhibited strong sensitivity to serum albumins. DNPM could bind to Sudlow site I and site II in HSA but could not be displaced from its binding sites by common site specific drugs (e.g. phenylbutazone and ibuprofen). Besides, DNPM exhibited great potential for illumining serum albumin in living cells. The results provided a beneficial approach for designing and synthesizing high sensitive and selective fluorescent probes for proteins.

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.

Development of an enhanced immunoassay based on protein nanoparticles displaying an IgG-binding domain and luciferase

Detection of small amounts of target molecules with high sensitivity is important for the diagnosis of many diseases, including cancers, and is particularly important to detect early stages of disease. Here, we report the development of a temperature-responsive fusion protein (ELP-DCN) comprised of an elastin-like polypeptide (ELP), poly-aspartic acid (D), antibody-binding domain C (C), and NanoLuc luciferase (N). ELP-DCN proteins form nanoparticles above a certain threshold temperature that display an antibody-binding domain and NanoLuc luciferase on their surface. ELP-DCN nanoparticles can be applied for enhancement of immunoassay systems because they provide more antibody-binding sites and an increased number of luciferase molecules, resulting in an increase in assay signal. Here, we report the detection of human serum albumin (HSA) as a model protein using anti-HSA and ELP-DCN proteins. Upon formation of ELP-DCN nanoparticles, the detection limit improved tenfold compared to the monomeric form of ELP-DCN.