A fluorescent sensor for discrimination of HSA from BSA through selectivity evolution

Biomimetic nanoplatforms constructed from dialkylaminostyryl hetarene dyes and phospholipids exhibiting selective fluorescent response to specific proteins

The present work explores the specificity of supramolecular assemblies comprising dialkylaminostyrylhetarene dye molecules incorporated into phosphatidylcholine (PC) or phosphatidylserine (PS) aggregates. In PS-based assemblies, the dyes demonstrate a concentration-dependent fluorescent response, distinguishing anionic proteins such as bovine serum albumin (BSA) and pepsin from lysozyme (LYZ) in aqueous solutions. Conversely, no significant response is observed when the dyes are incorporated into the well-organized bilayers of neutral PC. The fluorescent response arises from the binding of dyes to proteins, leading to the detachment of dye molecules from the assemblies, rather than from the binding of proteins to the assemblies, although the latter process is facilitated by electrostatic attraction. Thus, both the poor ordering of PS molecules and the interfacial arrangement of the dyes are prerequisites for the fluorescent response of dye-PS aggregates. The structure of the dyes significantly impacts the spectral features of dye-PS and dye-protein assemblies. An optimal dye structure has been identified for the recognition of BSA, with a limit of detection (LOD) of 10.8 nM.

A fluorescent "Turn-ON" probe with rapid and differential response to HSA and BSA: quantitative detection of HSA in urine

The present study provides insight into the differential response of a benzimidazole-malononitrile fluorescent "Turn-ON" probe on interaction with two structurally similar proteins, BSA and HSA. Compound 6 shows more sensitivity towards the two SAs, which is completely lost in the case of compound 7, synthesized by substitution on 6. The aggregates of compound 6 show absorption maxima at 385 nm and weak emission maxima at 565 nm. Compound 6 forms a new emission band at 475 nm on gradual addition of BSA (200 μM) along with a slight increase in the emission band at 565 nm. However, on addition of HSA (50 μM), a new band at 475 nm is formed. In contrast to BSA, in the case of HSA, 50% quenching is observed in the emission band of compound 6 at 565 nm. The new band formed on the interaction of 6 with BSA shows four-fold more enhancement compared to HSA. Furthermore, the mechanism of interaction of 6 with serum albumin has been investigated through lifetime-fluorescence analysis, site-selective drug experiments, dynamic light scattering, FE-SEM, FT-IR, etc. Molecular docking studies and site marker drug displacement experiments reveal differential interactions of 6 towards the two structurally similar proteins. Aggregates of 6 with an average hydrodynamic size of 100-190 nm are disassembled on adding BSA and HSA, and the size of the serum albumin and 6 complex decreases to 10-20 nm, revealing the ligand's encapsulation in the serum albumin cavity. Practical applicability for the quantitative detection of HSA in human urine samples is also demonstrated. The high binding affinity, sensitivity, selectivity and differential response of probe 6 towards two serum albumins (HSA and BSA) and significant quantification of HSA in urine samples shows the potential ability of this probe in medical applications.

Design and synthesis of a TICT-based red-emissive fluorescent probe for the rapid and selective detection of HSA in human biofluids and live cell imaging

Here, we report the design and synthesis of a D⋯π⋯A-based fluorescent probe, (E)-4-(4-(dibutylamine)-2-hydroxystyryl)-1-methylquinolin-1-ium (DHMQ), which is nonfluorescent in ∼100% PBS buffer medium due to a twisted intra molecular charge transfer (TICT) phenomenon and it becomes highly fluorescent (∼149 fold) in the presence of human serum albumin (HSA), owing to the restriction of its intramolecular free rotation inside the hydrophobic binding cavity of HSA. The site-selective fluorescence displacement assay and molecular docking studies clearly reveal that DHMQ selectively binds at subdomain IB of HSA. The 3σ/slope method was adopted to determine the limit of detection (LOD) value, which was as low as 2.39 nM in ∼100% PBS medium, indicating its high sensitivity towards HSA. The low dissociation constant value [Kd = (1.066 ± 0.017) μM] suggests a strong complexation between the DHMQ and HSA. Importantly, it has been demonstrated that DHMQ is capable of detecting HSA in real human serum and urine samples and was found to be suitable for live cell imaging of HSA.

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.

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.

Rational design of a FA1-targeting anti-interference fluorescent probe for the point-of-care testing of albuminuria

Albuminuria is a crucial urine biomarker of human unhealthy events such as kidney diseases, cardiovascular diseases, and diabetes. However, the accurate diagnosis of albuminuria poses a significant challenge owing to the severe interference from urine fluorescence and urine drugs. Here, we report a novel flavone-based fluorescent probe, DMC, by incorporating the FA1-targeting methylquinazoline group into a flavone skeleton with the extend π-conjugation. DMC exhibited a rapid response time, high sensitivity, and selectivity towards human serum albumin (HSA) in urine. Moreover, the red-shifted fluorescence and the FA1-targeted HSA-binding of DMC efficiently mitigated the interference from both urine fluorescence and urine drug metabolites. Furthermore, the establishment of a portable testing system highlighted the potential for point-of-care testing, offering a user-friendly and accurate approach to diagnose A2-level and A3-level albuminuria. We expect that the success of this DMC-based diagnostic platform in real urine samples can signify a significant advancement in early clinical diagnosis of albuminuria and its associated diseases.

HSA over BSA: Selective detection of Human Serum Albumin via a naphtho [2,1-b] furan-based system

Human serum albumin (HSA) is an important biomarker that can be used for the early diagnosis of many diseases. In this work, a TICT probe bearing fused naphtho-furan scaffold (NPNF) was developed and employed in the selective turn-on sensing of HSA. The probe's selectivity towards HSA was observed using steady-state fluorescence experiments, with limit of quantitation in micromolar levels. NPNF's capability to exclusively detect HSA over BSA was further studied/rationalized using anisotropy and time-resolved studies. Molecular docking was used to shed light on the location of NPNF in the subdomain IB of HSA. The practical application of the probe was also demonstrated by the detection of HSA in urine and the HSA-assisted detection of cerium.

A human serum albumin-binding-based fluorescent probe for monitoring hydrogen sulfide and bioimaging

In this work, a fluorescent probe, TPABF-HS, was developed for detecting hydrogen sulfide (H2S) using a human serum albumin (HSA)-binding-based approach for amplifying the fluorescence signal and extending the linear correlation range. Compared to the most recent probes for H2S, the most interesting feature of the detection system developed herein was the especially wide linear range (0-1000 μM (0-100 eq.)), which covered the physiological and pathological levels of H2S. TPABF-HS could be used in applications high sensitivity and selectivity with an LOD value of 0.42 μM. Further, site-competition experiments and molecular docking simulation experiments indicated that signal amplification was realized by the binding of the TPABF fluorophore to the naproxen-binding site of HSA. Moreover, the extension of the measurement span could allow for applications in living cells and Caenorhabditis elegans for imaging both exogenous and endogenous H2S. This work brings new information to the strategy of signal processing by exploiting fluorescent probes.

Development of New Thiophene-Containing Triaryl Pyrazoline Derivatives as PI3Kγ Inhibitors

A series of new thiophene-containing triaryl pyrazoline derivatives, 3a–3t, were synthesized and evaluated regarding PI3K inhibition activity and anti-tumor potency based on a trial of introducing significant moieties, including pyrazoline and thiophene, and simplifying the parallel ring structures. Most of the tested compounds indicated potent PI3K inhibitory potency, with this series of compounds showing more potency for PI3Kγ than PI3Kα. The top hit 3s seemed more potent than the positive control LY294002 on inhibiting PI3Kγ (IC₅₀ values: 0.066 μM versus 0.777 μM) and more selective from PI3Kα (Index values: 645 versus 1.74). It could be inferred that the combination of para- and meta-, as well as the modification of the electron-donating moieties, led to the improvement in potency. The anti-proliferation inhibitory activity and the enzymatic inhibition potency indicated consistent tendencies. The top hit 3s could inhibit the phosphorylation of Akt by inhibiting PI3K through the PI3K-Akt-mTOR pathway. The molecular docking simulation indicated that the binding pattern of 3s into PI3Kγ was preferable than that of PI3Kα, with more hydrogen bond, more π-involved interactions, and fewer π-sulfur interactions. The information in this work is referable for the further development of selective inhibitors for specific isoforms of PI3K.

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.

A novel target and biomarker benzothiazolyl-naphthalimide probes for precisely and selective detection of serum albumin and anticancer activity

N-Benzothiazolyl-1,8-naphthalimide based fluorescence probes were designed and synthesized for selective detection of human serum albumin (HSA) and Bovine serum albumin (BSA) among various bioanalytes and further studied for their in...

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.

TICT-Based Microenvironment-Sensitive Probe with Turn-on Red Emission for Human Serum Albumin Detection and for Targeting Lipid Droplet Imaging

Fluorescent probes sensitive to microenvironment have always been fascinating due to their tremendous advantages in tracking changes in the pathophysiological microenvironment and potential application in the early diagnosis of related diseases. In this study, a fluorescent luminogen, triphenylamine-thiophene-rhodanine (TPA-TRDN), with high sensitivity to changes in polarity and viscosity was designed and could be applied to detecting human serum albumin (HSA) in actual urine, as well as lipid droplets (LDs) in cells and in vivo with turn-on red emission. TPA-TRDN could selectively detect HSA with fast response (10 min), superior sensitivity (LOD 0.34 μg/mL, about 60-fold fluorescence enhancement), and wide detection range (0.00-0.30 mg/mL). The detection mechanism was demonstrated: TPA-TRDN encountered the hydrophobic IB domain of HSA, leading to the inhibition of the twisted intramolecular charge transfer (TICT) phenomenon and intramolecular rotation. Moreover, TPA-TRDN demonstrated satisfactory ability to identify cancer cells and noncancer cells by microenvironment-guided specific LD bioimaging. This evidence indicated that TPA-TRDN has promising application in the microenvironment-related biomedical field and clinical diagnosis.

Effects of Human Serum Albumin on the Fluorescence Intensity and Tumor Imaging Properties of IR-780 Dye

IR-780 is a lipophilic dye with excellent optical and tumor imaging properties for early tumor diagnostics. Although the mechanism of tumor targeting has not been fully identified, the view that serum albumin plays an important role in tumor accumulation has been recognized. Here, the mechanism of the interaction between IR-780 and HSA was studied to explore the effect of albumin on its tumor targeting properties. Data demonstrate that IR-780 can be tightly adsorbed by HSA at a ratio of 1:1 to form a noncovalent complex, which exhibits significant improvement in the near-infrared fluorescence imaging and tumor diagnosis capacity. During this process, the endogenous fluorescence and esterase activity of HSA are both partially inhibited by IR-780, and the α-helical content of HSA slightly increases. Molecular docking simulation displays that the binding site of IR-780 on HSA is between subdomains IIA and IIB. These results indicate that HSA is an important factor to mediate the optical performance of IR-780, giving it higher tumor diagnosis capability.

A berberrubine-derived fluorescent probe for hydrazine and its practical application in water and food samples

In this work, we attempted to develop a fluorescent probe for hydrazine in real samples. Accordingly, we designed BER9-HZ to fulfill the set rules as solubility, anti-interference capability and functional compatibility. The selected reporting group BER9 dissolved 100% within 10 min, which indicated much better solubility than Berberine. The 615 nm reporting signal was in the Near-Infrared region. BER9-HZ presented advantages including wide linear range (0-20 equivalent), high sensitivity (detection limit 0.076 μM), steadiness (pH 7.0-13.0, temperature 25-45 °C), rapid response (within 20 min) and high selectivity in both independent and co-existing systems. Significantly, BER9-HZ could work steadily in real environmental, plant and food samples, thus be used in the detection of hydrazine (directly incubated or pre-treated with real sample) in living cells. Therefore, this work marched one step further to the systematic managing of hydrazine in real samples, and raised useful information for future investigations on Nitrogen circulation.

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.

How human serum albumin-selective DNA aptamer binds to bovine and canine serum albumins

Serum albumin (SA) is the most abundant carrier protein in blood. SA carries a diverse range of nutrients, drugs, and metal ions. It has wide clinical and biochemical applications. Human serum albumin (HSA) can be used as a biomarker for kidney and liver diseases. Aptasensor is one of potential HSA detection methods. HSA-specific aptamer was selected for HSA detection. In animals, bovine serum albumin (BSA) and canine serum albumins (CSA) share high sequence similarities to HSA. Thus, it is interesting to explore the possibility of using HSA-selective aptamer for BSA and CSA aptasensor. In this study, molecular dynamics (MD) simulations were initially employed to investigate the binding of aptamer to BSA and CSA in comparison to HSA. Like HSA, both BSA and CSA can bind aptamer, but different binding affinities are observed. BSA shows the tighter binding to aptamer than CSA. Domain III is found to be the aptamer-binding domain although no specific aptamer conformation is captured. However, in all cases, the aptamer utilizes the 3'-end to attach on an albumin surface. Both nucleobases and phosphate backbones on a DNA aptamer are important for albumin-aptamer complexation. Our results imply the possibility of using HSA-specific aptamer for BSA detection due to tighter binding observed, but may be less effective in CSA. However, the test in actual complicated condition must be further studied.

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.