Fluorescence Of Bovine Serum Albumin Research Articles

Interaction Study between ESIPT Fluorescent Lipophile-Based Benzazoles and BSA.

In this study, the interactions of ESIPT fluorescent lipophile-based benzazoles with bovine serum albumin (BSA) were studied and their binding affinity was evaluated. In phosphate-buffered saline (PBS) solution these compounds produce absorption maxima in the UV region and a main fluorescence emission with a large Stokes shift in the blue–green regions due to a proton transfer process in the excited state. The interactions of the benzazoles with BSA were studied using UV-Vis absorption and steady-state fluorescence spectroscopy. The observed spectral quenching of BSA indicates that these compounds could bind to BSA through a strong binding affinity afforded by a static quenching mechanism (Kq~1012 L·mol−1·s−1). The docking simulations indicate that compounds 13 and 16 bind closely to Trp134 in domain I, adopting similar binding poses and interactions. On the other hand, compounds 12, 14, 15, and 17 were bound between domains I and III and did not directly interact with Trp134.

Structural exploration of interactions of (+) catechin and (−) epicatechin with bovine serum albumin: Insights from molecular dynamics and spectroscopic methods

The interaction of two stereoisomeric flavanols (+) catechin (CT) and (−) epicatechin (ECT) with bovine serum albumin (BSA) has been studied using UV–Vis absorption and fluorescence spectroscopy. The binding affinity between flavanols and BSA is investigated through fluorescence quenching. Fluorescence study shows that both flavanols exhibit a strong interaction with BSA at a single binding site. This investigation indicates that CT/ECT may quench BSA fluorescence by the static quenching process due to the formation of ground state complex. The binding pocket of BSA is identified at the site I/II with the interaction of CT/ECT using molecular docking studies. Molecular dynamics simulation (MDS) reported the structural changes of BSA into sturdy α-helix formations owing to the interaction of CT/ECT. During the 200 ns simulation, BSA-ECT complex had lower root mean square deviation values, and undergoes slight structural deformations. The MDS result shows that the binding of CT/ECT with BSA is due to hydrophobic and hydrogen bond interactions, which supports the experimental outcomes. The analysis of radius of gyration confirmed that the BSA-ECT complex possessed a more compact structure. CT and ECT differ in their binding site and structural effects caused by distinct orientational positions at the benzopyran moiety. These findings help us to understand the binding nature of CT/ECT with BSA protein, and the effect of protein during blood transportation process.

A mutispectroscopic study on the structure–affinity relationship of the interactions of bisphenol analogues with bovine serum albumin

Bisphenol A (BPA) is a recognized endocrine-disrupting chemical (EDC), and its analogues also exert negative effects on health. The structure–affinity relationship between the structures of nine bisphenol (BP) analogues and the conformational changes of bovine serum albumin (BSA) was studied by various characterization methods and molecular docking. BPs including BPA and its analogues, bisphenol B (BPB), bisphenol C (BPC), bisphenol AP (BPAP), bisphenol M (BPM), bisphenol P (BPP), bisphenol Z (BPZ), diethylstilbestrol (DES) and dienestrol (DS) interacted with BSA. At the concentration of 3.85 × 10−5 mol l−1, DS was found to lead to 64% quenching, while BPAP, BPM and DES quenched 60%, 59% and 55% of BSA fluorescence, respectively. The values of ΔH (−19.31–135.42 kJ mol−1) and ΔS (12.52–495.63 J mol−1 K−1) indicated that hydrophobic interactions and hydrogen bonds played important roles in the binding process. The binding constants of DS (8.87 × 104 l mol−1), DES (3.05 × 104 l mol−1), BPAP (1.52 × 104 l mol−1), BPC (1.16 × 104 l mol−1) and BPM (1.10 × 104 l mol−1) to BSA were greater than that of BPA (1.18 × 103 l mol−1) to BSA, indicating that they may exert more negative effects than BPA. The molecular structure differences of these BPs partly affected their ability to bind to BSA. The binding constants of BPB/BPP to BSA were smaller due to the steric hindrance of ethyl and benzene ring. BPs with conjugated double bond structures (DS and DES) and benzene ring structures (BPM, BPP, BPAP) had a greater influence on the conformation of BSA.

Green synthesis and characterization of Fe doped ZnO nanoparticles and their interaction with bovine serum albumin

Herein we report an eco-friendly and cost efficient synthesis of Fe doped ZnO (TPFZO) nanoparticles using the extract of Thespesia polpulanea flowers as a stabilizing agent. The synthesized NPs have been characterized by XRD, FT-IR, UV-DRS, SEM, EDAX and TEM studies. The synthesized NPs were found to have the crystallite size in the range of 30–60 ​nm. The calculated band gap energies for ZO and TPFZO nanoparticles were 3.00 ​eV and 1.97 ​eV respectively. The size distribution of the ZO and TPFZO obtained from TEM were observed to be lying in the range 50–120 ​nm and 4–22 ​nm respectively. The interaction of TPFZO NPs with bovine serum albumin (BSA) has been studied using fluorescence and absorption titration methods. The results indicated that the nanoparticles quenched the BSA fluorescence at 340 ​nm via static quenching mode having a bimolecular quenching rate constant value of 6.21 ​× ​1013 Lmol−1s−1.

Exploring the Noncovalent Interactions of the Dinuclear Cu(II) Schiff Base Complex with Bovine Serum Albumin and Cell Viability against the SiHa Cancer Cell Line.

In the present study, a dinuclear bis(μ-acetate) dicopper(II) complex [Cu2L2(μ1.1-CH3COO-)2] has been synthesized from a tridentate NNO Schiff Base ligand L (L = 2,4-dibromo-6-((3-(methylamino)propylimino)methyl)phenol) and characterized by elemental, ultraviolet-visible (UV-vis), Fourier transform infrared (FTIR), 1H NMR, and electrospray ionization-mass spectrometry (ESI-MS) spectroscopic studies. The single-crystal X-ray structure, different noncovalent interactions, Hirshfeld surface analysis, and density functional theory (DFT) studies of the dinuclear complex were determined by crystallographic computational studies. The structural study exposed that the complex consists of the penta-coordinated double μ1.1-acetato-bridged dinuclear units of Cu(II), and it is a centrosymmetric dimer in which the center of inversion lies at the midpoint of two Cu(II) ions. Hirshfeld surface and DFT studies pointed out the probable potentiality of the crystal in prospective binding with the protein. This was experimentally verified by carrying out the binding interaction studies against bovine serum albumin (BSA) protein using various spectroscopic methods. It was observed that the copper(II) complex could strongly bind to BSA and could quench the intrinsic fluorescence of BSA. Further, the studied complex was appraised for cell viability studies against SiHa cancer cells. It is observed that cell viability increases with time, demonstrating the biocompatible nature of the complex.

The interaction of folate-modified Bletilla striata polysaccharide-based micelle with bovine serum albumin.

We fabricated an amphiphilic folate-modified Bletilla striata polysaccharide (FA-BSP-SA) copolymer that exhibited good biocompatibility and superior antitumor effects. This study investigated the affinity between FA-BSP-SA and bovine serum albumin (BSA) via multispetroscopic approaches. Changes in the morphology and particle size showed that FA-BSP-SA formed a blurry "protein corona". Stern-Volmer equation demonstrated that FA-BSP-SA micelles decreased the fluorescence of BSA via static quenching. The measurement results of thermodynamic parameters (entropy change, enthalpy change, and Gibbs free energy) suggested that the binding between FA-BSP-SA and BSA was spontaneous in which Van der Waals forces and hydrogen bonding played major roles. The results from synchronous fluorescence, circular dichroism, and UV spectra also revealed that BSA conformation was slightly altered by decreasing α-helical contents. In addition, the antitumor effects in vitro of Dox@FA-BSP-SA micelles and the cellular uptake behavior of micelles in 4T1 cells were decreased after incubating with BSA.

Multi-Spectroscopic, thermodynamic and molecular dynamic simulation studies for investigation of interaction of dapagliflozin with bovine serum albumin

Dapagliflozin (DAPA) is a selective sodium-glucose cotransporter-2 inhibitor that reduces renal glucose reabsorption. The drug has recently become a crucial milestone in the management of diabetes and heart failure. In this study, the interaction of DAPA with bovine serum albumin (BSA) was investigated for the first time using various fluorescence spectroscopic techniques, UV-absorption spectroscopy, molecular docking, and molecular dynamic (MD) simulation. The fluorescence spectroscopic titration study performed at different temperatures showed that DAPA quenched the fluorescence of BSA through a combination of dynamic and static mechanisms, which was confirmed by UV absorption, fluorescence-resonance energy transfer measurements, and MD simulation. The binding thermodynamic parameters demonstrated that the binding stoichiometry between BSA and DAPA was 1:1. Competitive binding experiments using site-specific markers as well as molecular docking studies showed that DAPA binds to site I on BSA. The positive values of enthalpy change (ΔH) and entropy change (ΔS) revealed that hydrophobic forces played a predominant role in the binding of DAPA to BSA, whereas the negative value of Gibbs free energy change (ΔG) indicated the spontaneity of the interaction. Moreover, the synchronous fluorescence spectroscopy has shown that DAPA binding to the protein molecule occurs in the vicinity of the tryptophan residue. These findings were confirmed by the molecular docking and MD simulation studies.

Study of the binding mechanism between hydroxytyrosol and bovine serum albumin using multispectral and molecular docking

Hydroxytyrosol (HT) is a naturally occurring amphiphilic plant polyphenol with tremendous potential as an antioxidant, antibacterial, anti-cancer, cardiovascular disease treatment, etc. However, the mechanisms of its interactions with proteins remain unclear. The interaction between HT and bovine serum albumin (BSA) in vitro was investigated through multispectral spectroscopy, molecular docking, particle size studies, and atomic force microscopy (AFM). Fluorescence spectra and molecular docking results indicated that HT was bound to the active site of BSA via hydrophobic forces through a spontaneous binding process (ΔG<0). A single HT binding site was observed on BSA, which was located in the hydrophobic cavity between Domain ⅡA and Domain ⅡB near the Trp213 residue, leading to the static quenching of endogenous BSA fluorescence. Synchronous fluorescence spectroscopy revealed that HT primarily quenched the fluorescence of Trp213 residues of the BSA. Three-dimensional fluorescence spectra confirmed the conformational alteration of BSA treated with HT, which was further supported by Ultraviolet–Visible spectra. Raman spectra showed that the α-helix content (from 36.420% to 59.968% at BSA:HT ratios of from 1:0 to 1:30, respectively) had a more obvious increase with higher HT concentrations. The solution particle sizes increased as the HT concentration increased. However, the AFM results suggested that HT had a negligible contribution toward changing the BSA microstructure. These results will provide reference materials for the wider application of HT and further research into protein-polyphenol interactions.

Exploring the interaction of bavachin and its glycoside derivatives with bovine serum albumin using spectroscopic and molecular docking approaches

Bavachin (BVN) is a flavonoid extracted from the traditional Chinese medicine Psoralea corylifolia Linn. (P. corylifolia). BVNglu1-3 are three synthesised novel glycoside derivatives of bavachin with good water solubility. In this study, the interactions of BVN and BVNglu1-3 with bovine serum albumin (BSA) were explored using a combination of spectroscopy and molecular docking techniques. The experimental results showed that BVN and its glycoside derivatives (BVNs) formed stable complexes with BSA, leading to the intrinsic fluorescence quenching of BSA. BSA fluorescence quenching primarily occurred via the static mechanism. The binding constants of BVNs with BSA were in the order of BVN (2.66 × 105) ≫ BVNglu2 (1.66 × 103) > BVNglu1 (1.49 × 103) > BVNglu3 (0.84 × 103) at 298 K. The effects of the glycoside group number and position on binding affinity have been discussed. Analysis of the thermodynamic parameters demonstrated that the binding interactions of BVNs with BSA were spontaneous. BVN and its glycosides showed different modes of interaction forces when bound to BSA. Conformational experimental research revealed that the binding of the four compounds affected the secondary structure of BSA marginally. The site competition experiments and molecular docking studies showed that BVN and its glycosides did not share the same binding sites on BSA.

Exploring the interactions of acenaphthene with bovine serum albumin: Spectroscopic methods, molecular modeling and chemometric approaches

The interaction of acenaphthene (ACN), a widespread environmental pollutant, with bovine serum albumin (BSA) was explored using spectroscopic methods, molecular modeling and chemometric approaches. The multivariate curve resolution-alternating least squares (MCR-ALS) analysis decomposed the overlapped excitation-emission matrix (EEM) spectra of mixture of ACN and BSA successfully and extracted spectral profiles of pure BSA, ACN and BSA-ACN complex. Based on fluorescence quenching analysis, ACN quenched the inherent fluorescence of BSA remarkably via a static mechanism. The obtained value of binding constant (Kb = 3.82 × 105 L mol−1) revealed a high binding affinity of ACN to BSA which facilitates its distribution by blood circulation system. Furthermore, the binding parameters values revealed that one binding site in BSA was involved in BSA-ACN complex. FT-IR, UV–Vis and CD spectra showed that the conformation of BSA was altered in presence of ACN slightly. Molecular docking simulation suggested that ACN was located in the IA region of BSA and the main interactions between ACN and BSA, are van der Waals forces. The obtained results provide some insight into interactions between ACN and serum albumins at the molecular level.

Molecular insight on the binding of stevia glycosides to bovine serum albumin

The interaction of the steviol and its glycosides (SG), steviolbioside, and rebaudioside A, with bovine serum albumin (BSA) was studied by absorption and fluorescence spectroscopy techniques alongside molecular docking. The stevia derivatives quenched the fluorescence of BSA by a dynamic quenching mechanism, indicating the interaction between the stevia derivatives and BSA. The binding constant (Kb) of steviol was 100-1000-fold higher than those of SG. The stevia derivative/BSA binding reaction was spontaneous and involved the formation of hydrogen bonds and van der Waals interactions between steviol and steviolbioside with BSA, and water reorganization around the rebaudioside A/BSA complex. Molecular docking pointed out the FA1 and FA9 binding sites of BSA as the probable binding sites of steviol and SG, respectively. In conclusion, steviol enhanced hydrophobicity and small size compared to SG may favor its binding to BSA. As steviol and its glycosides share binding sites on BSA with free fatty acids and drugs, they may be competitively displaced from plasma albumin under various physiological states or disease conditions. These findings are clinically relevant and provide an insight into the pharmacokinetics and pharmacodynamics of the stevia glycosides.

Silver-enhanced fluorescence of bimetallic Au/Ag nanoclusters as ultrasensitive sensing probe for the detection of folic acid

Folic acid (FA) is the natural form of water-soluble vitamins widely found in most plants and animal products and its deficiency leads to several human body abnormalities. The advancements of metal nanoclusters are highly increasing due to their molecule-like optical properties and attractive applications. Because of increasingly demand of noble metal nanoclusters as sensing templates, different synthesis methods have been developed for facile synthesis of noble metal nanoclusters. Herein, red-emitting fluorescent bovine serum albumin (BSA)-capped Au–Ag bimetallic NCs are facilely synthesized through green one-pot synthetic approach. The effect of silver on the fluorescence properties of Au NCs was investigated and it was found that introduction of silver can enhance the fluorescence intensity. The fluorescence intensity of the as-prepared Au–Ag nanoclusters gets quenched in the presence of folic acid in an aqueous medium and it was used as ultrasensitive sensing probe for FA detection. The developed Au–Ag NCs-based sensing probe shows linear response in the wide range of 0–100 μM and the detection limit is as low as 0.47 nM. Its applicability has also been confirmed successfully in real human serum, urine and FA tablet samples. Due to the high stability, sensitivity and selectivity, the developed bimetallic cluster sensing system is highly promising to be applied in the pharmaceutical and clinical laboratories.

The fluorescence spectroscopic study on the interaction between 3-ethyl-benzothiazospironaphthopyran and bovine serum albumin

The interaction of 3-ethyl-benzothiazospironaphthopyran (BSNP) with bovine serum albumin (BSA) was analyzed by fluorescence spectroscopy. Firstly, the optimal experimental conditions, including medium, pH and ionic strength, were investigated. Secondly, the fluorescence titration experiments at 298 K, 306 K, and 313 K showed that the intrinsic fluorescence of BSA can be strongly quenched by the small organic molecule BSNP. The formation of a BSA-BSNP complex suggested that the fluorescence quenching mechanism may be a kind of static quenching procedure. Finally, the binding constants (K) and the ratio of fluorescence quantum yields of BSA-BSNP complex and free BSA (f) at three different temperatures were obtained. The values of the former were 7.91×104 L mol-1, 6.60×104 L mol-1, and 5.22×104 L mol-1. The values of the latter is 0.88, 0.98, and 1.00.

Molecular interactions of cefoperazone with bovine serum albumin: Extensive experimental and computational investigations

We investigated the binding of the cephalosporin-class drug cefoperazone (CFP) with bovine serum albumin (BSA) using spectroscopic techniques and in silico methods. The aim of this study was to (i) emphasize the importance of correcting for the inner filter effect in this type of study and (ii) understand the binding mechanism of CFP with BSA by addressing protein conformation and plausible binding sites. Formation of the complex was confirmed by UV–visible spectroscopy. Quenching of BSA fluorescence in the presence of CFP was also observed. Because of the high absorption of CFP in the fluorescence emission range of BSA, the fluorescence emission spectra were corrected for the inner filter effect. Fluorescence emission was studied at excitation wavelengths of 280 and 295 nm. The uncorrected data showed a significant contribution of tyrosine at the excitation wavelength of 280 nm; however, after correction, this contribution became negligible. The static-type mechanism was found to be involved in quenching, with almost 1:1 binding between BSA and CFP. Hydrogen bonding and hydrophobic forces were found to dominate the protein–ligand interactions with a slight decrease in the α-helical contents. Synchronous fluorescence spectral data (at Δλ = 15 and 60 nm) were also corrected for the inner filter effect, with the results being similar to those of excitation at 280 and 295 nm. Molecular docking and molecular dynamics (MD) simulation results suggest that, apart from the two known drug binding sites (drug site I and II), one putative binding site (binding site III) located between BSA domains 1 and 3 was also possible for CFP. MD simulations of the previously reported drug binding sites (drug site I and II) and putative binding site III revealed that binding site III showed excellent binding profiles and could be a target for future research related to BSA-drug binding.

Interactions of Ag+ ions and Ag-nanoparticles with protein. A comparative and multi spectroscopic investigation

UV–visible and florescence spectroscopic methods have been applied to analyze the binding capabilities of Ag+ ions and AgNPs with bovine serum albumin (BSA). UV–visible studies revealed that BSA acted as a ligand towards both Ag+ and AgNPs, and provides potential site for coordination. BSA fluorescence was quenched significantly by the quenchers (Ag+ and AgNPs). The binding constant, quenching constant, quantum yield, and coordination sites were evaluated. The Ag+ ions has strong binding and quenching efficiency towards BSA than that of AgNPs. The distance between the tryptophan and acceptor decreases from 127 Å to 72 Å with Ag+ ions from 0.6 to 20.0 × 10-5 mol/L. The energy transfer from BSA to ligand (Ag+ ions and AgNPs) follows a surface energy transfer process with a 1/d4 distance dependence. This is found to be according to strong coordinating affinity of metal ions with structural unit of protein, which helps to understand the mechanism of bacterial cell death in presence of metal ions and/or metal NPs.

Design and synthesis of ferrocene‐tethered pyrazolines and pyrazoles: Photophysical studies, protein‐binding behavior with bovine serum albumin, and antiproliferative activity against MDA‐MB‐231 triple negative breast cancer cells

We report synthesis and characterization of a series of ferrocene‐pyrazoline and pyrazole hybrids and demonstrate their biomedical applications. All new compounds were identified with the help of spectroscopic techniques and single‐crystal X‐ray analysis. The compounds from both the series show fluorescent activity. The effect of C5 aryl substituent on the luminescent behavior of the parent system was followed by studying their absorption and emission behavior. The binding affinity of a selected ferrocenyl pyrazoline with C5 2‐naphthyl substituent (4g) to bovine serum albumin (BSA) was examined through fluorescence quenching experiments using excitation wavelength 290 nm. The ligand 4g quenched the intrinsic fluorescence of BSA. Strong binding between 4g and BSA was observed with equilibrium constant for the complex formation of the order of 105 M‐1. In vitro anticancer activity of a series of ferrocenyl‐pyrazolines and pyrazoles (4f, 4g, 4h, 5f, 5g, and 5h) was tested against hormone‐independent triple negative breast cancer cells MDA‐MB‐231 in which maximum inhibition potency was noted for 4h with IC50 value of 3.61 mg ml−1.

Studies on the interaction of salicylic acid and its monohydroxy substituted derivatives with bovine serum albumin

Salicylic acid and its monohydroxy substituted derivatives are usually used as food additives. They can interact with bovine serum albumin (BSA) through π-π stacking, the monohydroxy substitutions can hinder the interactions through steric effects. In this paper, we systematically studied the interactions between BSA and salicylic acid and its monohydroxy substituted derivatives under simulative physiological conditions by diverse spectroscopic methods and molecular docking studies. The spectroscopic studies showed that the intrinsic fluorescence of BSA could be quenched by salicylic acid and its derivatives. The quenching mechanism is a combination of static and dynamic quenching. Furthermore, the molecular docking simulation revealed the binding sites (near the Trp-213 in the BSA) and the distance (2.1 nm, 2.9 nm, 2.0 nm, 2.7 nm and 3.3 nm, respectively) between ligand and protein, which is in good agreement with the calculated results of the energy transfer process. Our research may provide guidance for understanding the interactions between serum albumin and salicylic acid food additives.

Interaction of AMOT@CS NPs and AMOT drug with bovine serum albumin: Insights from spectroscopic and molecular docking techniques

The drug binding to serum protein (SP) is an area of intense research in evaluating drug candidates. Thus, composite material based on chitosan (CS), and amoxicillin tri hydrate (AMOT) were designed in order to evaluate the release of AMOT@CS NPs and it’s binding with BSA under physiological condition. The inclusion of 2% v/v T80 in the CS NPs enabled in vitro release of AMOT, at 298 K and pH 7.4 up to 68.03%. This study also was undertaken to compare and explore the binding of potential chemotherapeutic antibacterial drug Amoxicillin trihydrate (AMOT) and AMOT@Chitosan nanoparticles (AMOT@CS NPs) with a model protein bovine serum albumin (BSA) by fluorescence spectroscopy, synchronous fluorescence spectroscopy, Ultraviolet–visible (UV–vis) absorption, and CD spectroscopic techniques. Experimental results indicated that AMOT and AMOT@CS NPs could bind with BSA and quench the fluorescence of BSA via static mechanism. The interactions among BSA with AMOT, AMOT/T80 and AMOT@CS NPs were evidenced by substantial changes in the BSA secondary structure, as revealed by circular dichroism. The findings of thermodynamic parameters revealed that the binding reaction in both systems was exothermic and spontaneous, enthalpically driven and that the hydrogen bonding and Vander Waals forces played a vital role to achieve optimal interaction between AMOT/ AMOT@CS NPs and BSA.

Measuring Single-Cell Platelet Forces via Microcontact-Printed, Reference-Free Traction Force Microscopy Reveals Relationships between Cell Shape, F-Actin Localization, and Force

Platelets bind, spread, and contract to stop bleeding and reinforce hemostatic plugs. Platelet contraction occurs when interactions between actin and myosin create cytoskeletal tension and force generation. In this study, single-cell platelet forces were measured using a novel microcontact-printed, reference-free traction force microscopy approach. This approach facilitates single-cell force measurement on a contiguous topology that enables unrestricted platelet spreading without necessitating platelet removal to calculate force. Microcontact printing is used to deposit a grid of fluorescent bovine serum albumin onto a flexible polydimethylsiloxane substrate. Platelets from healthy donors were washed and seeded onto von Willebrand Factor-coated substrates. Platelets were fixed, stained, and imaged via confocal microscopy to simultaneously visualize fluorescently labeled platelets and grid displacement (used to calculate single-cell force.) Because microcontact-printing facilitates printing the grid on large, scalable surfaces, platelet forces were able to be measured on >100 single-cells per donor (N = 6 donors). Donor-to-donor platelet force variability was examined, and some donors produce significantly more force per platelet than other donors (p<0.01). Even within each donor, ∼15-fold variability in single platelet forces exists. A well-established area-force relationship (more spread cells produce more force) accounts for some variability in force generation, but for cells spread equally, there is still ∼5-fold differences in force generation. After examining the relationship between cell shape and force, a relationship was observed wherein platelets that are more circular produce more force. Additionally, amongst spread platelets, platelets with more spread F-actin produce more force. This versatile method that facilitates measurement of single-cell forces over large areas without restricting cell spreading or requiring cell removal reveals donor variability, cell shape, and F-actin localization as contributors to the large variability of single-platelet forces.

Bimodal Endocytic Probe for Three-Dimensional Correlative Light and Electron Microscopy

Correlative light and electron microscopy (CLEM) can infer molecular, functional and dynamic information to ultrastructure by linking information of different imaging modalities. One of the main challenges, especially in 3D-CLEM, is the accurate registration of fluorescent signals to electron microscopy (EM). Here, we present fluorescent BSA-gold (fBSA-Au), a bimodal endocytic tracer as fiducial marker for 2D and 3D CLEM applications. fBSA-Au consists of colloidal gold (Au) particles stabilized with fluorescent bovine serum albumin (BSA). The conjugate is efficiently endocytosed and distributed throughout the 3D endo-lysosomal network of the cells, and has an excellent visibility both in fluorescence microscopy (FM) and EM. We demonstrate the use of fBSA-Au in several 2D and 3D CLEM applications using Tokuyasu cryosections, resin-embedded material, and cryo-EM. As a fiducial marker, fBSA-Au facilitates rapid registration of regions of interest between FM and EM modalities and enables accurate (50-150 nm) correlation of fluorescence to EM data. Endocytosed fBSA-Au benefits from a homogenous 3D distribution throughout the endosomal system within the cell, and does not obscure any cellular ultrastructure. The broad applicability and visibility in both modalities makes fBSA-Au an excellent endocytic fiducial marker for 2D and 3D (cryo-)CLEM applications.