Spectroscopic Studies on the Thermodynamics of L-Cysteine Capped CdSe/CdS Quantum Dots—BSA Interactions

Abstract

CdSe/CdS quantum dots (QDs) capped with L-cysteine can provide an effective platform for the interactions with bovine serum albumin (BSA). In this study, absorption and fluorescence (FL) spectroscopy were used to study the binding reactions of QDs with BSA, respectively. The binding constant (≈10(4) M(-1)) from FL quenching method matches well with that determined from the absorption spectral changes. The modified Stern-Volmer quenching constant (5.23 × 10(4), 5.22 × 10(4), and 4.90 × 10(4) M(-1)) and the binding sites (≈1) at different temperatures (304 K, 309 K, and 314 K) and corresponding thermodynamic parameters were calculated (∆G < 0, ∆H < 0, and ∆S < 0). The results show the quenching constant is inversely correlated with temperature. It indicates the quenching mechanism is the static quenching in nature rather than dynamic quenching. The negative values of free energy (∆G < 0) suggest that the binding process is spontaneous, ∆H < 0 and ∆S < 0 suggest that the binding of QDs to BSA is enthalpy-driven. The enthalpy and entropy changes for the formation of ground state complex depend on the capping agent of QDs and the protein types. Furthermore, the reaction forces were discussed between QDs and BSA, and the results show hydrogen bonds and van der Waals interactions play a major role in the binding reaction.

Multi-spectroscopic techniques to evaluate the toxicity of alloyed CdSeS quantum dots

“…With the addition of CdSeS QDs, the absorption intensity of BSA increased gradually along with a slight blueshift from 278 nm to 276 nm, reconfirming that there is the ground state complex formation between BSA and CdSeS QDs because dynamic quenching does not change the absorption spectra while the formation of ground state complex, that is, static quenching often leads to a change in the absorption spectra [22]. Similar results were also observed in the study of L-cysteine capped CdSe/CdS QDs and thioglycolic acid capped CdTe QDs on BSA [13,33]. The blue shift of absorption peaks showed the peptide strands of BSA molecules extended more and the hydrophobicity was decreased [12][13]31].…”

“…Zhao et al investigated the biological toxicity of CdTe QDs to BSA via fluorescence spectra, UV-vis absorption spectra and circular dichroism (CD) and showed the addition of CdTe QDs changed the conformation of BSA [12]. Ding et al proved that L-cysteine capped CdSe/CdS QDs quenches the fluorescence of BSA through the formation of ground state complex [13]. Ghali illustrated that static quenching was responsible for BSA fluorescence quenching upon conjugation with small sized CdS QDs (4.4 nm) [14].…”

Interaction via in situ binding of CdS nanorods onto gelatin

“…The binding mechanism between nanomaterials and protein with respect to binding constant, binding site number, thermodynamic parameters, and nature of the binding forces was investigated, and preliminary results show that the binding process is spontaneous between capped CdS nanoparticles and protein [6,[9][10][11]. However, Asha Jhonsi et al [5] discovered the interaction between uncapped CdS and BSA is very weak.…”

“…However, Asha Jhonsi et al [5] discovered the interaction between uncapped CdS and BSA is very weak. So the studies on capped CdS nanoparticles using various capping agents, such as thioglycerol [9], L-cysteine [11] and starch [12,13], are significant for the interaction between nanoparticles and protein. Although a lot of researches have focused on the interactions between nanomaterials and proteins, little attention has been paid to the interactions of the endogenous nanomaterials with globular proteins, particularly the nanomaterials with fibrous proteins [14,15].…”

Interaction of CdTe Quantum Dots with 2,2-Diphenyl-1-Picrylhydrazyl Free Radical: A Spectroscopic, Fluorimetric and Kinetic Study

“…They exhibit tunable and intense fluorescence spectra [1][2][3][4][5], broad excitation spectra and favourable photostability [6][7][8][9]. Imaging and sensing applications have been proposed for QDs [7,[10][11][12].…”