Recent Advances of Organic Fluorescent Probes for Detection of Human Serum Albumin

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.

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.

Intermolecular proton transfer from flavonol to human serum albumin triggers a red-shifted ratiometric fluorescence response

Intermolecular proton transfer from a flavonol-based probe to the arginine (Arg222) in drug site 1 of human serum albumin triggers an unusual red-shifted ratiometric fluorescence response, which can be applied in the point-to-care diagnosis of hypoalbuminemia.

The first fluorescent sensor for the detection of closantel in meat

Closantel is widely used in the management of parasitic infestation in livestock, but is contraindicated in humans due to its high toxic to human retina. Thus, development of a fast and selective method for the detection of closantel residues in animal products is highly needed yet still challenging. In the present study, we report a supramolecular fluorescent sensor for closantel detection through a two-step screening process. The fluorescent sensor can detect closantel with a fast response (<10 s), high sensitivity, and high selectivity. The limit of detection is 0.29 ppm, which is much lower than the maximum residue level set by government. Moreover, the applicability of this sensor has been demonstrated in commercial drugs tablets, injection fluids, and real edible animal products (muscle, kidney, and liver). This work provides the first fluorescence analytical tool for accurate and selective determination of closantel, and may inspire more sensor design for food analysis.

Rapid Point-of-Care Quantification of Human Serum Albumin in Urine Based on Ratiometric Fluorescence Signaling Driven by Intramolecular H-Bonding

Human serum albumin exerts multifunctions, such as maintaining the oncotic pressure of plasma, carrying hydrophobic molecules, and acting as the most important antioxidant in the blood. Lower serum albumin levels are linked to several cardiovascular diseases, and dysfunction of albumin reabsorption in the kidney is linked to liver disease, renal disorder, and diabetes. Albumin is thus a powerful diagnostic and prognostic marker; however, its quantification in urine by readily affordable tools is challenging owing to its very low concentration. To address this issue, we developed a ratiometric fluorescent probe with multiple advantages through a systematic structure variation of a benzocoumarin fluorophore and, further, a prototype of a smartphone-based point-of-care device. We determined albumin levels in urine and observed that a smoking person has notably higher urine albumin than a nonsmoking person. The cheap device provides a promising tool for albumin-associated disease diagnosis in communities with limited resources.

Fluorescence discrimination of HSA from BSA: A close look at the albumin-induced restricted intramolecular rotation of flavonoid probe

Discrimination of human serum albumin (HSA) from bovine serum albumin (BSA) based on the fluorescence probe technique is still challenging due to similar chemical structures. In this work, a novel flavonoid-based fluorescent probe AF is reported for successful discrimination of HSA from BSA. The sensing performances of probe, including sensing dynamic, sensitivity and selectivity, have been carefully studied. Moreover, sensing mechanism was elucidated by Job's plot, displacement experiment, and molecular docking, suggesting that the specific response to HSA originated from the albumin-induced restricted intramolecular rotation (RIR) of probe. This work may provide a simple way for designing of novel probes for HSA with high selectivity.

Design, synthesis and mechanistic studies of a TICT based fluorogenic probe for lighting up protein HSA

Human serum albumin (HSA) in blood serves as an important biomarker for clinical diagnosis, and fluorescence sensing method has attracted extensive attention. In this work, a small organic molecule probe, YS8, involving twisted intramolecular charge transfer (TICT) characteristic, was designed and investigated to detect HSA. YS8 kept silent state in fluorescence under physiological conditions, but the encapsulation of YS8 in the hydrophobic subdomain IB region of HSA inhibited the TICT state and produced a clear light-up fluorescent signal. Especially, YS8 was demonstrated to be an efficient fluorogenic probe to discriminate HSA from other proteins including the bovine serum albumin (BSA). Moreover, YS8/HSA complex could be applied in fluorescence imaging in living cells and is also useful in the study of artificial fluorescent protein (AFP).

A DS2-specific flavonoid-based probe with a unique dual-emissive response to human serum albumin

The hydroxyl substituent in flavonoids can cause the binding site to change from DS1 to DS2 and restore the ESIPT process of flavonoids, thereby leading to a unique dual-emissive response towards human serum albumin.

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.