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Studying the interactions of bioactive phenolic acids [ferulic acid (FA), caffeic acid (CA), and chlorogenic acid (CGA)] with the carrier protein bovine hemoglobin (BHb) helps to understand their modes of binding and transport, which affect their bioavailability. The protein–ligand complexes exhibited binding constants (Kb) in the range of 104 M−1, indicating a reversible mode of association. BHb–CA complexation attenuated the inherent fluorescence of BHb (β2-Trp37 dominant fluorophore) through a static quenching mechanism. However, a combined (static and dynamic) quenching mechanism was observed for the BHb–FA/CGA complexes. In this study, the thermodynamic parameter, ΔG°, determined from fluorescence spectroscopy, was negative, suggesting that the complexation of BHb with phenolic acids was spontaneous. The negative change in enthalpy [ΔH° = –(8.539 ± 1.331) kJ mol−1, –(10.620 ± 1.028) kJ mol−1, and –(8.637 ± 0.232) kJ mol−1 for BHb–FA, BHb–CA, BHb–CGA complexes, respectively] and positive entropy change [ΔS° = + (63.862 ± 1.218) J mol−1 K−1, +(67.108 ± 1.681) J mol−1 K−1, and +(62.540 ± 1.058) J mol−1 K−1 for BHb–FA, BHb–CA, BHb–CGA complexes, respectively] indicated that hydrogen bonding and hydrophobic forces stabilized the complexes. Computational studies also illustrated similar interactive forces in BHb–ligand complexes. Changes around the microenvironment of the Trp residues in the binding process were verified using various spectral measurements. Circular dichroism and Fourier infrared spectroscopies illustrated a decrease in the α-helical content of BHb during complexation. Fibril inhibition properties of the ligands were verified using ThT assay, ANS binding studies, Congo Red assay, turbidity assay, Soret absorption measurements, and CD spectral measurements. The structure–activity relationship, binding affinity, and interactive forces between the protein and phenolic acids could explain the order of anti-fibrillation properties. [ABSTRACT FROM AUTHOR]

In recent decades, Cd-based quantum dots (QDs) have gained tremendous interest as luminescence tags for numerous biological applications. However, chemical synthesis using organic molecules to encapsulate the QDs surface is a highly complex process, high-cost and aggressive fabrication, and less aqueous and biocompatible, which leads to restricted biological applications. In this paper, we have reported the biogenic synthesis of CdSe-HSA core and CdSe@ZnSe-HSA core–shell QDs for the first time using human serum albumin protein as a surface engineering molecule. The biosynthesized QDs were found to be smaller in size (2–3.5 nm) and highly aqueous compatible (stable for up to 150 days). The biosynthesized QDs act as ultrasensitive fluorescence probes for label-free sensing of Hg2+ with enhanced efficiency, and an LOD value of 1.3 nM for CdSe@ZnSe-HSA QDs (concentration range: 0–2 μM) was obtained and were also able to detect with the naked eye. A dynamic quenching mechanism was observed for the fluorescence quenching of the biosynthesized QDs by Hg2+ ions, and affinity toward the formation of Hg–Se or Hg–SH with the QDs provided the unique selectivity. Moreover, the smaller size and unique surface properties of the biosynthesized QDs contributed to the enhanced antibacterial properties against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria and found more effective against Gram-negative bacteria. This work implies the biogenic aqueous compatible synthesis of core and core–shell QDs for biological and environmental monitoring analytical methods for the development of bionanotechnology. [ABSTRACT FROM AUTHOR]

This study focuses on synthesizing an injectable and self-healing hydrogel from an abundant serum protein (bovine serum albumin, BSA) to control antimicrobial drug delivery impeding bacterial infections. Hydrogels were synthesized through a green synthesis route without using any crosslinking agent and characterized for their cross-linking, surface morphology, self-healing, viscoelasticity, injectability, and swelling and degradation properties. The prepared hydrogel has distinctive autofluorescence properties, as observed from the wavelength-dependent steady-state fluorescence spectral measurements. When lomefloxacin and doxycycline were incorporated into the hydrogel network, it allowed the controlled release of both antibiotics over at least 24 hours, with a release rate of over 90%. Hydrogels containing lomefloxacin and doxycycline were effectively used against E. coli and E. faecalis bacterial strains; their antibacterial effects were maintained for 24 hours. The live/dead cell test indicated that the hydrogel is effective against both (Gram-positive and Gram-negative) bacteria strains. Furthermore, our studies on bacteria encapsulation, specifically using E. coli, confirmed that the hydrogel is non-toxic, and the hydrogel demonstrates biocompatibility as the bacteria successfully grow within the hydrogel matrix. To assess biocompatibility, we conducted a cell attachment experiment with HEK 293 cells, and the results suggest that this hydrogel could be used for 3D cell culturing in the future. [ABSTRACT FROM AUTHOR]

Biocompatible quantum dots (QDs) have attracted a lot of attention due to their potential biological applications (drug delivery, sensing and diagnosis). Here, we have synthesized 2–4 nm sized biocompatible zinc sulphide (ZnS) QDs using a plant leaf extract as an immobilizing and stabilizing agent via a green route. We have investigated the biological effects of ZnS QDs in a variety of applications, including (1) anti-bacterial activity, (2) cell cytotoxicity, (3) bio-sensing and (4) protein binding. Studies on the anti-bacterial activity of the as-synthesized ZnS QDs against E. coli and E. faecalis inhibited bacterial growth effectively and showed a cytotoxic effect on the HeLa cell line. The biosynthesized ZnS QDs act as a fluorescence probe to detect bilirubin and rifampicin (RFP) with a wide linear range, high sensitivity, good selectivity, and a low limit of detection (LOD), with LOD values of 22.12 ± 0.25 ng mL−1 and 122.37 ± 0.42 ng mL−1, respectively. In a biological matrix, the QDs can form a complex with biomacromolecules; therefore, we studied the interaction between a carrier protein (HSA) and the as-synthesized ZnS QDs. The surface functionalized and nano-sized ZnS-GT QDs were observed to form complexes with the human serum albumin (HSA) protein and quenched the intrinsic fluorescence of HSA through static and dynamic quenching modes. The binding affinity was observed to be of the order of 105 M−1 for the HSA–ZnS-GT QD interactions, which can be considered as a reversible mode of binding. The effect of the ZnS QDs on other ligands and protein interactions was also studied. Enhanced binding affinities for HSA–quercetin ((5.994 ± 0.139) × 105 M−1) and HSA–luteolin ((3.068 ± 0.127) × 105 M−1) interactions were also observed in the presence of ZnS-GT QDs. [ABSTRACT FROM AUTHOR]