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

A red-emissive tripodal nanoprobe for the discrimination of serum albumin with conformational change from Y- to ω-like and probing mitochondrial viscosity

Serum albumins, such as bovine serum albumin (BSA) and human serum albumin (HSA), play a crucial role in various biological processes. Discrimination between BSA and HSA is challenging due to their similar structures and reactivity. Here, we report mitochondria-targeted red fluorescent tripodal nanoprobe DMAS-TP, forming spherical nano-aggregates (∼90 nm) in water for discrimination of BSA over HSA and detection and imaging of viscosity in HeLa cells. DMAS-TP exhibits an ∼56-fold fluorescence intensity increase in 95% glycerol compared to water, which indicates restricted movement in high-viscosity solvents. Furthermore, the addition of 5 equiv. BSA and HSA to DMAS-TP solution displays ∼50-fold and ∼10-fold fluorescence intensity increases at 630 nm (λex 490 nm), respectively, and can detect as low as 20 nM BSA and 140 nM HSA. The fluorescence anisotropy plot shows that the DMAS-TP anisotropy values decrease from 0.234 to 0.185 with increasing [BSA/HSA], suggesting a conformational change from Y- to ω-like structure. The fluorescence lifetime of DMAS-TP increases gradually with BSA/HSA, suggesting dynamic complexation. DMAS-TP aggregates diminish to 6 nm particles when encapsulated in BSA confirmed by DLS, SEM, and TEM, with reduced fluorescence intensity in the presence of bilirubin, indicating that DMAS-TP binds within the BSA cavity near site IB. DMAS-TP is highly permeable to HeLa cells and shows a strong affinity for mitochondria, making it suitable for imaging viscosity and BSA via strong fluorescence in the red channel.

Tetraphenylethylene-indole as a novel fluorescent probe for selective and sensitive detection of human serum albumin (HSA) in biological matrices and monitoring of HSA purity and degradation

Human serum albumin (HSA) levels in serum and urine is a crucial biomarker for diagnosing liver and kidney diseases. HSA is used to treat various disorders in clinical practice and as an excipient in the production of vaccine or protein drug, ensuring its purity essential for patient safety. However, selective and sensitive detection of HSA remains challenging due to its structural similarity with bovine serum albumin (BSA) and the inherent complexity of biological matrices. This study presents a novel application of the tetraphenylethylene-indole (TPE-indo) fluorophore for the identification and quantification of HSA. The findings demonstrate that TPE-indo binds specifically to HSA in a 1:1 M ratio, thereby triggering its aggregation-induced emission (AIE) mechanism and producing a selective, sensitive, and rapid "turn-on" fluorescence response. The fluorescence intensity of TPE-indo exhibited minimal interference from proteins, amino acids, sugars, ions, and urine metabolites, and demonstrated a linear correlation with HSA concentration up to 60 μg/mL, with a limit of detection of 0.30 μg/mL. Furthermore, TPE-indo displays a markedly enhanced response to HSA in comparison to BSA, which can be ascribed to the distinct binding modes between TPE-indo and these two proteins. TPE-indo can be used to quantify HSA in serum, grade proteinuria samples, detect BSA adulteration in HSA samples, and real-time monitor HSA degradation processes. This study not only advances the development of efficient HSA detection methods but also highlights the significance of TPE-indo as a versatile tool for bioanalysis and clinical diagnosis.

A-D-A type fluorescent probe with dual quaternary-ammonium-salt anchors for turn on detection of HSA in wide emission gamut

Human serum albumin (HSA) is a key protein implicates in various physiological and pathological conditions such as renal injury, diabetes mellitus. Herein, we report an AIE-active fluorescent probe (DNI-4) for detection of HSA with a "turn on" response covering visible and near-infrared region (500 - 800 nm). Combining with a triphenylamine and two 1,8-naphthalimide moieties, the chromophore segment of DNI-4 forms a "A-D-A" type molecular architecture with the twisted intramolecular charge transfer property. Two quaternary ammonium salt moieties are introduced into the chromophore to give the probe (DNI-4), which has good hydrophilicity and can interact with HSA to form the dye-HSA aggregates with "turn-on" signal. DNI-4 demonstrates a good linear correlation over a low concentration range of HSA from 0 to 0.2 μM (R2 = 0.9995), with a limit of detection (LOD) as low as 15 nM. We tested the diameters and potential values of DNI-4 and HSA to disclose the variation in microstructure before and after the recognition event. Furthermore, we test and compare the sensitivity and association constants of DNI-4 and two control compounds, neutral DNI-1 and mono-quaternary-ammonium-salt-substituted DNI-5. The results indicate the electronic interaction is a key factor for recognition and DNI-4 with the most positive groups is the best probe for HSA. At last, DNI-4 is successfully applied to probe HSA in the Hela cells indicating the potential application in fluorescent sensing and bioimaging.

Assessing the environmental risks of sulfonylurea pollutants: Insights into the risk priority and structure-toxicity relationships

Sulfonylureas are widely used herbicides globally; however, the health risks associated with exposure to these compounds are poorly understood. This study used fuzzy clustering to categorize 44 sulfonylurea compounds into three risk priority levels (I, II, and III) and further investigated their structure-toxicity relationships. The order of the risk priority levels was level I＜level II＜level III. The pecking order of protein affinity was on the order of 104 M-1, which was consistent with the order of the risk priority levels. Moreover, toxic conjugations induced significant changes in protein conformation, with high-risk sulfonylurea causing substantial conformational changes. Given that the conformations of sulfonylurea within the reactive domain were highly similar, the patterns of toxic actions were considerably similar as well. Structure-toxicity relationship analysis indicated a positive correlation among Gibbs free energy change (ΔG°), affinity between sulfonylurea and protein, logarithm of the octanol-water partition coefficient (logKow), and risk priority. Specifically, a higher ΔG° value corresponded to stronger affinity, and a higher logKow value corresponded to a higher environment risk. The electronegativity of the aromatic ring on the left side of the sulfonylurea molecule is a key determinant influencing affinity - higher electronegativity of this aromatic ring weakened the affinity of sulfonylurea for protein and reduced the risk. When the aromatic ring on the left side of sulfonylurea was consistent, an increase in the electronegativity of the heterocyclic ring on the right side resulted in a stronger affinity for protein and an increased risk. This study provides a mechanistic foundation for evaluating the health risks associated with exposure to sulfonylurea.

A self-assembled fluorescent nanoprobe recognized by FA1 site for specifically selecting HSA: Its applications in hemin detection, cell imaging and fluorescent tracing drug delivery

As naturally essential biomacromolecule, HSA has become diagnostic indicators for various diseases and universal carriers for anticancer drug delivery, therefore, fluorescence detection and labeling for HSA possess significant application value in the biomedical field. In this paper, hydrazide Schiff base fluorescent probe NDQC was designed and synthesized, which self-assembled into nanoparticles in aqueous solution system and demonstrated excellent selectivity and sensitivity towards HSA. Through displacement assay and molecular docking simulation, the binding of NDQC with HSA in FA1 site was demonstrated, thereby no obvious fluorescence signal presented for homologous protein BSA due to their structural differences in binding site. Non-toxic probe NDQC is suitable for the fluorescence imaging of HSA in cells, and colocalization fluorescence images showed that NDQC-HSA could illuminate mitochondria. Based on the pH sensitivity of fluorescence emission for NDQC-HSA, discrimination of cancer cells and normal cells could be achieved. For practical applications, NDQC-HSA can be employed to measure the content of hemin. More importantly, NDQC could fluorescently label HSA and therefore NDQC-HSA complex act as the carrier for loading cisplatin. The present findings demonstrate that the probe NDQC has potential in exploring HSA at cellular levels and hold great promise in application of tracking drug-loading nanoparticles.

Bridged triphenylamine-based fluorescent probe for selective and direct detection of HSA in urine

Human serum albumin (HSA) serves as a crucial indicator for therapeutic monitoring and biomedical diagnosis. In this study, a near infrared (NIR) fluorescent probe, termed BTPA, characterized a donor-π-acceptor (D-π-A) structure based on bridged triphenylamine (TPA) was developed. BTPA exhibited outstanding sensitivity and selectivity towards HSA among various analysts, with a remarkable 50-fold fluorescence enhancement with a significant Stokes shift (∼190 nm) and a wide linear detection range of 0-20 μM of HSA. Especially, BTPA displayed selectivity for discrimination of HSA from BSA. Job's Plot analysis suggested a 1:1 stoichiometry for the formation of the BTPA-HSA complex. Displacement assays and molecular docking demonstrated that BTPA binds to subdomain IB of HSA which could effectively avoid interference from most drugs. Besides, BTPA have good biocompatibility and could detect of exogenous HSA with a relatively low fluorescence background. For practical applications, BTPA was tested for detecting HSA levels in human urine without any pretreatment, showing detection capability in the range of 0-10 μM with a fast response (<30 s), a limit of detection (LOD) of 0.12 μM and good recoveries (81.7-92.9 %), highlighting the high performance of bridged triphenylamine-based probe BTPA.

Sensitive and accurate monitoring of urinary albumin and point-of-care testing using a fluorescent probe with anti-interference capacity against exogenous drugs

Fluorescent probes have been reported for monitoring urinary albumin (u-ALB) to enable early diagnosis of kidney diseases and facilitate regular point-of-care testing (POCT) for chronic kidney disease (CKD) patients. However, the albumin can bind hydrophobic drugs through host-guest interactions, which may result in decreased accuracy of probes at regular drug sites and hamper POCT of albuminuria since CKD patients often need to take medications routinely. Herein, we reported a novel fluorescent probe (NC-2) by molecular engineering of a reported AIEgen (NC-1). The introduction of a non-conjugated ring moiety to the molecular rotor granted the NC-2 enhanced sensitivity with a limit of detection in urine of 8.7 mg/L, which is below l the threshold of microalbuminuria (30 mg/L). Moreover, the NC-2 was found to preferentially bind to the FA1 site of ALB, conferring it with excellent anti-interference capacities against exogenous drug molecules and metabolites. Simulation experiments using lab-spiked urine samples containing common drugs taken by CKD patients demonstrated that the probe could provide satisfied detecting accuracy (80-90 %). Furthermore, a paper-based device was constructed and achieved on-site detection of u-ALB in qualitative and semi-quantitative manners. Findings in this work were of great significance to the development of fluorescent probes for accurate detection of ALB in complex urine samples and the further achievement of fluorescence-based POCT for CKD.

1,4-Dihydropyridine-based FA1 site-specific fluorescent probes for the selective detection and quantification of HSA levels in biofluids

Human serum albumin (HSA) is a multifunctional circulatory protein essential for many physiological processes including oncotic pressure maintenance, ligand/drug binding and transport, antioxidant activity, etc. Abnormal HSA levels in biological fluids have been reported in a variety of clinical disorders, making it a potential biomarker for early diagnosis. Low serum albumin levels have been linked to increased long- and short-term mortality rates in ICU patients. Therefore, quantifying HSA in biofluids such as serum and urine offers a convenient approach for the early identification of underlying clinical conditions and assessing the risk factors. Herein, we report a series of fluorescent 1,4-dihydropyridine (DHP) derivatives for the detection and quantification of HSA in biofluids. Their response towards HSA can be tuned by varying the substituents at the C-4 and the N-1 of the DHP ring. Depending on the nature of the substituents, they generated either a turn-on or ratiometric response with a LoD in low nanomolar or subnanomolar levels. A pair of enantiomers obtained by introducing a chiral center on the N-substituents highlighted the importance of stereochemistry in HSA-ligand interactions. Quantification of HSA in complex biofluids, such as blood serum and urine, was also accomplished using these probes. The high selectivity of some of the probes towards HSA over the homologous BSA allowed the discrimination of these two proteins. The preferred binding location of the probes was the hemin binding site and the detection mechanism was identified as the restriction of intramolecular rotation. Additionally, a prototype of a smartphone-integrated point-of-care device was also fabricated to demonstrate the feasibility of utilizing these probes in clinical settings.

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.

Mirror-Image Human Serum Albumin Domain III as a Tool for Analyzing Site II-Dependent Molecular Recognition

Human serum albumin (HSA) as a drug carrier can significantly improve the pharmacokinetic profiles of short-lived therapeutics. Conjugation of albumin-binding moieties (ABMs) to therapeutic agents may prolong their serum half-life by promoting their association with endogenous HSA. To discover a new molecular class of ABMs from mirror-image chemical space, a preparation protocol for bioactive HSA domain III and its d-enantiomer (d-HSA domain III) was established. Structural and functional analyses suggested that the synthetic protein enantiomers exhibited mirror-image structures and stereoselective neonatal fragement crystallizable receptor (FcRn) recognition. Additionally, the ligand-binding properties of synthetic l-HSA domain III were comparable with those of site II in native HSA, as confirmed using site II-selective fluorescent probes and an esterase substrate. Synthetic d-HSA domain III is an attractive tool for analyzing the site II-dependent molecular recognition properties of HSA.

Harnessing a simple ratiometric fluorescent probe for albumin recognition and beyond

A commercially available naphthalene fluorophore serves as a ratiometric indicator for albumin, showcasing its applications in albumin-based supramolecular recognition.

Ratiometric determination of etomidate based on an albumin-based indicator displacement assay (IDA)

The first fluorescent sensor based on the indicator displacement assay (IDA) for on-site determination of etomidate.