Carbon Dots in Biomedical Applications: A Review of Their Interaction with Serum Albumins, Antidepressant Agents, and Enzymatic Systems

Reshma^a, Bhanushree Gupta^a*

^a Center for Basic Sciences, Pt. Ravishankar Shukla University Raipur (C.G.), India 492010

Abstract

Carbon dots (CDs) are a type of carbon-based nanoparticles that can be categorized into subtypes based on their structure and morphology. These nanoparticles possess adjustable physical, chemical, and optical characteristics, which can be easily manipulated through simple one-pot synthesis methods. CDs are highly attractive due to their biocompatibility, non-toxic nature, resistance to photobleaching and chemical degradation, and cost-effectiveness, making them suitable for a wide array of applications. Their synthesis can be carried out using two main strategies: (i) top-down approaches and (ii) bottom-up approaches. Both strategies allow for the customization of chemical structures to achieve desired band gaps, doping with heteroatoms, and functional groups. Ongoing studies continue to shed light on how the structure of CDs influences their optical behavior. In the previous study, the interactions between bovine serum albumin (BSA) and human serum albumin (HSA) with antidepressant drugs—namely amitriptyline hydrochloride (AMT), chlorpromazine hydrochloride (CPZ), and desipramine hydrochloride (DSP)—bioconjugated  and acetylcholinestarase enzymes on carbon dots (CDs), were investigated using various spectroscopic techniques. The photoluminescence of CDs is influenced by several factors, including the synthesis route, precursor materials, surface characteristics, and the type of heteroatom doping. This review explores different synthesis techniques and examines the resulting optical, physical, chemical, and structural properties of CDs. Moreover, it discusses their potential applications in fields such as biomedicine, LEDs, anti-counterfeiting, and sensing, with particular emphasis on the challenges faced in sensing and possible solutions to address them.

Keywords – Carbon dots, serum albumins, acetylcholinesterase, antidepressants, desipramine hydrochloride

1.0  Introduction

Nanotechnology is an innovative field of science and technology concerned at the nanoscale, i.e., dimensions between approximately 1 and 100 nm [1-3]. Nanoparticles are classified according to diameter, viz. liposomes, polymeric nanoparticles, dendrimers, fullerenes, quantum dots, metal nanoparticles, magnetic nanoparticles and semiconductor nanoparticles [4-6]. Carbon dots (C-dots) have recently attracted great interest for their unique properties of tunable photoluminescence, stable fluorescence, low toxicity, and favorable biocompatibility [7-10]. On the other hand, C-dots have been shows the promising supports for construction of optical sensors for quantitative assay of biomolecules and environmental pollutants, while zero-dimensional (0D) C-dots having excellent properties associated with quantum confinement [11-14].

Carbon-based nanomaterials including carbon nanoparticles(quantum dots), nanocrystals, nanotubes, fullerenes, nanofibers, graphene nanosheets and porus carbon materials have proising application in nanoelectronics, microelectrical devices, electrochemistry, sensors catalysis, utracapacitors, bioimagaing, and drug deliver[15-17]. Fluorescent carbon nanoparticles (CNPs) or nanodots (CDs) constitute a fascinating class of recently discovered nano carbon with a size below 10 nm and have attracted considerable research interest due to their excellent photostability, superior biocompatibility, minimal toxicity and excellent water solubility. As a consequence of their outstanding properties, CNPs or CDs from attractive applications[18,19]. CDs induce same blue or green photoluminescence, they are still comparatively very low compared to that of the fluorescent carbon quantum dots. 

The synthesis of environmentally benign carbon nanoparticles and carbon quantum dots with high photoluminescence properties is still a great challenge. Carbon quantum dots have been synthesized various methods such as hammers methods, one pot methods, candle soot method, laser induced pyrolysis of hydrocarbons, low temperature solution synthesis, electrochemical oxidation of graphite, microwave pyrolysis of sucrose, proton-beam irradiation of nanodiamonds, thermal decomposition of organic compounds, using mesoporus silica nanoparticles as template and using polyacrylo nitrile (PAN) as a nanoparticle precursor. Although those methods are available for the synthesis of CNPs and CDs, the one-pot method, the candle soot and microwave pyrolysis of sucrose are the useful techniques because they are economically feasible.

The interfacing of C-dots with biomolecules such as protein is useful for application ranging from nanobiotechnology (molecular diagnostics) to medicine (therapeutic and drug delivery) [15-20]. A better understanding of the biological effects requires knowledge of the binding properties of proteins that associate with the C-dots [21, 22]. The affinity of protein towards C-dots is regulated by its surface properties through chemical composition, shape and surface functionalization [23-25]. Currently, attention has been driven towards the development of protein-based C-dots due to high biocompatibility and site-specific delivery [26-28].

The major advantage of nanoparticles as a delivery system are in regulating size of particles, surface properties and release of pharmacologically active agents in order to attain the site-specific action of the drugs. [29-31]. It is making significant improvement in biomedical applications, including newer drug delivery technology. There has been considerable research in developing biodegradable nanoparticles as effective drug delivery systems [32-35]. The quantum dots-based drug interactions are applied for biomedical, biosensing and forensic field [36, 37].

1.1 Drugs

In recent years, drug pharmacology, therapeutic effects, drug chemical structures and genomic information have been introduced to characterize the drug–target interactions. Many drugs particularly those with local anesthetic, tranquilizer, antidepressant, and antibiotic action, exert their activity by interaction with biological membranes. Thus, by protein carrier these drugs have to be carried to their sites of action at which they bind with different affinities.  In plasma strong binding can decrease the concentration of free drug because weak binding can lead to a low circulation time or poor distribution [39-41].  The nature and dynamics of binding to small molecules represent an active area of investigation. The most suitable, economic and frequently used oral route of drug administration, but poor gastrointestinal membrane permeability it’s a major drawback. Penetration enhancers may be incorporated into various formulations in order to overcome the problem of low permeability and bioavailability of drugs across the biological membranes [42,43].

The pharmacological effect of drug molecules is usually manifested at low concentration where self-association is not important; it is likely that accumulation of drug molecules at certain sites in the body may cause a localized high concentration, resulting in aggregation and subsequent changes in biological activity due to their decreased ability to pass through biological barriers [44,45]. This excess number of drugs can cause over-stimulation, psychotic illness and other disorders. The targeted drug-delivery in body organs is necessary and for these purpose cosolvent, complexing agents, liposome formulations, emulsions and solid dispersions can be used as drug-carriers [46,47].

1.1.1 Antidepressants Drug

 Antidepressants are a class of drug that reduces symptoms of depressive disorders by correcting chemical imbalances of neurotransmitters in the brain; chemical imbalances may be responsible for change in mood and behavior [48,49]

Neurotransmitters are vital, as they are the communication link between nerve cells in the brain. Neurotransmitters reside within vesicles found in nerve cells, which are released by one nerve and taken up by other nerves. This process is called "reuptake." The prevalent neurotransmitters in the brain specific to depression are serotonin, dopamine and norepinephrine [50-51].

In general, antidepressants work by inhibiting the reuptake of specific neurotransmitters, hence increasing their levels around the nerves within the brain, such as selective serotonin reuptake inhibitors (SSRIs), antidepressants that will affect serotonin levels in the brain [51, 52]. Antidepressants are used to treat several conditions. They include depression, generalized anxiety disorder, agitation, obsessive compulsive disorders (OCD)[23], manic-depressive disorders, childhood enuresis (bedwetting)[24], major depressive disorder, diabetic peripheral neuropathic pain, neuropathic pain, social anxiety disorder, post-traumatic stress disorder (PTSD) etc[25, 26].

1.1.2 TYPES OF ANTIDEPRESSANT DRUG

There are different types of drugs used in the treatment of depression, including selective serotonin reuptake inhibitors (SSRIs), atypical antidepressants, tricyclic antidepressants (TCAs), and monoamine oxidase inhibitors (MAOIs).

The different types of antidepressant drugs are shown in flow chart 1.

Chart 1. Types of antidepressant drugs.

1.1.3 Tricyclic antidepressant

Amitriptyline hydrochloride (AMT) (scheme I) is a first-generation antidepressant drug, presents the tricyclic antidepressant suffers from several draw-backs like anticholinergic, cardiovascular, and antiarrhythmic side effects [27]. To reduce these side effects, the antidepressants are used with a drug carrier.

Scheme I. Chemical Structures of Amphiphilic Drugs

Imipramine hydrochloride (IMP) (scheme 1) is one of the tricyclic drugs [28] that has a great variety of biological and chemical properties, being commonly used in clinics as antidepressant and antipsychotic drug. Under physiological conditions, it is amphiphilic cationic compound, which consists of a hydrophobic nitrogen-containing heterocyclic bound to a short chain containing a charged amino group [29, 30].

The physical and chemical properties of chlorpromazine hydrochloride (CPZ) (scheme 1) in aqueous solutions have been studied in detail (Scholtan, 1955), and the drug is soluble at a wide range of concentrations and ionic strengths [31-33]. A large number of drug molecules are amphiphlic and self-associates in aqueous environment to form small aggregates. Their “surfactant-like” behaviour is due to the presence of an almost planar tricyclic ring system and a short hydrocarbon chain carrying a terminal nitrogen atom [34].

1.2 PROTEIN

A protein is a naturally occurring complex and large biological molecule that is composed of one or more chains of amino acids (AAs). Proteins are involved in every aspect of living organism and obviously without protein living things would not exist. Proteins are linear chains of AAs that adopt a unique three-dimensional structure in their native state [35, 36]. This native structure allows the protein to carry out its biochemical function. There are amazingly versatile biological roles of proteins that from the basis for life. They help in full functioning of the body, some of them, for example, include various enzymatic and chemical reactions in the body [53]. Each of the thousands of naturally occurring proteins has its own characteristic, amino acid (AA) composition and sequence that results unique three-dimensional shape. How each protein performs its specific function in the body depends on its AA sequences [54, 55].

Over the past few decades protein-drug interactions have been a subject of extensive studies because they are of great importance in an extensive variety of industries, biological, pharmaceutical and cosmetic systems [35-37]. Globular proteins are main functional ingredients in healthcare and pharmaceutical products, through their capability to catalyze biochemical reactions, the surface of some substance to be absorbed and to bind other moieties and form molecular aggregation [38].  One of the most widely used globular protein is serum albumin, since it has a well-known primary structure and been associated with the binding of many different categories of molecules, such as dyes, drugs and toxic chemicals [39, 40].

1.2.1 Structural features of amino acids

Proteins are one primary building block of biological molecules and are comprised of small sub units known as amino acids (AAs). Understanding the structure and physical feature of AAs enable us to understand the structure and properties of proteins [41]. The ability of AAs to from a three-dimensional protein structure is significantly interesting and fascinating that combines the aspects of biophysical properties, structural features and the conformation of certain functional groups of biomolecules. The chemical features of a protein molecule are very complex, and are expected to be the sum of the properties of its constitute AAs in a protein chain [42-44].  AAs are virtually unique in forming linear macromolecules with a non-repetitive and a covalent-bonded structure. A chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H₂O) by a peptide bond [55].

1.2.2 Different levels of the protein structure

The Danish protein chemist K.U. Lindersrom-Long eluciadated three levels in proteins structure: primary, secondary and tertiary. Furthermore, J.D. Bernal included the quaternary structure in which the protein is composed of more than domain [46-48].

(A) Primary structure 

The primary structure is the number and sequence of AAs in a protein’s polypeptide chain or chains, each AA to the next by connecting the peptide bonds and starting with free amino group. By convention, the primary structure of a protein is a reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end shown in fig. 1. Clearly, the AAs sequence of protein, plus intra- and inter chain cross-links if any, defines the primary structure [48, 49].

Fig.1. Primary structure of  Bovine serum albumin (Source:http://www.rcsb.org/pdb/explore.do)

(B) Secondary structure

The secondary structure is an important level in the hierarchical classification of protein structure and it is used to identify protein features for fold recognition [50]. The secondary structure does not describe the actual folding of the protein in three dimensions, instead it illustrates the structure of small region of the peptide chain shown in fig 2. When two AAs are joined together, they form a planar structure where the bonds between AAs are able to rotate. Therefore, the AAs attempt to assume a structure that minimizes their free energy [51, 52].A part of the chain of AAs in a primary sequence twists and turns so that is backbone assumes a variety of stable secondary structures, which include helices, sheets, turns, and loops. There are possibilities of many regions of different secondary structure present in the same protein [53, 54].

Fig.2.Secondary Structure of Bovine serum albumin (Source:http://www.rcsb.org/pdb/explore.do)

(C) Tertiary structure

The tertiary structure of a protein contains the overall, unique, three-dimensional folding of a protein. The tertiary structure of a protein describes the folding of its secondary structural elements and specifies the positions of each atom in the protein, including those of its side chains [35-37]. Protein tertiary structures are the result of weak interactions include, ionic binding, hydrogen binding, hydrophobic interactions and disulfide bonds shown in fig. 3. Although, the three-dimensional shape of a protein seems irregular and random, it is fashioned by many stabilizing forces due to bonding interactions between the side-chain groups of the AAs. The protein is folded in such a way that its stability is not hampered in the presence of aqueous environment [38, 39].

Fig.3 Tertiary Structure of Bovine serum albumin (Source:http://www.rcsb.org/pdb/explore.do)

(D) Quaternary structure  

The formation of the quaternary structure in a protein is a remarkable phenomenon during which the units of tertiary structure arranged to form homo- or hetero- mutimers. This is found to be common in most of the proteins, especially in the case of enzymes [41-43]. As represented in Figure 4. The quaternary structure of a protein is an assembly of multiple polypeptide chains in one integral structure, the arrangement of which gives rise to a stable structure. Mainly by weak interaction (may be hydrophobic or ionic) of quaternary structure are stabilized between residues exposed on surface of the polypeptide in a protein. The presence of these large structures in a protein provides rigidity that is necessary to orient the substrate to enable catalysis by the biomolecule.

Fig.4. Quternary Structure of Bovine serum albumin (Source:http://www.rcsb.org/pdb/explore.do)

Serum albumin is the most abundant protein in blood plasma. Its principal function is to transport fatty acids, a great variety of metabolites, and drugs, such as anticoagulants, tranquilizers, and general anesthetics [44]. Serum albumins contribute to colloidal osmotic blood pressure and most importantly, play a key role in the transport of a wide variety of substances. 

Protein shows amphiphilic characters because of the hydrophobic and hydrophilic properties of the amino acids that cause amphiphilic molecules to interact with it. Serum albumin is a protein which is suitable sites for the binding of fatty acids, bilirubin, steroids, and a large number of dyes and drugs [45,46].

1.2.3 Folding or unfolding of proteins

The covalent structure of a natural protein is primarily composed of the 20 naturally occurring AAs. Different types of amino acids are present which is depend on their shape, size, charge, chemical activity, charge and affinity towards the hydrogen bond[30,31]. AAs having polarity or contain charges participated in the formation of hydrogen bond and electrostatic interactions in the presence of co-solvent or solvent. Whereas AAs having non-polarity shows unfavorable interactions with solvent molecule (especially water) [31-33].

Most of the proteins found in nature have to adopt a specific three-dimensional confirmation, called folded or native state for proper functioning, which is essential for performing their biological functions, Consisting the most importance of proteins in living organisms, the investigation of the structural and functional properties of proteins has always been a priority of biophysical chemists [35,36].

Understanding the protein folding process helps us to understand the behavior of the biomolecule and the obtained information is remarkable in overcoming the challenges in both modern biophysical and pharmaceutical contexts. The final result of protein folding, therefore, reflects the participation of several interdependent effects that give rise to structures of increasing complexity or intramolecular as in protein folding [36].

The folding of polypeptide chains to their native structures is an essential step in decoding genetic information to cellular activities and certain biological processes, because only the folded conformation of the protein is functioning. Native structure of biomolecules corresponds to the structure that is thermodynamically stable under physiological condition [37,38].

1.3 An Interaction of Drug with Proteins

More recently, the binding between proteins and antidepressant drug has been discussed. With regard to proteins, serum albumin is one of the most extensively studied serum albumins. Bovine serum albumins (BSA) and human serum albumin (HSA), which is an important transfer protein, are approximately 76% homologous and display a strictly conserved repeating pattern of disulfides [31]. Bovine serum albumin (BSA) being the major macromolecule in blood plasma of animals accounting to about 60% of the total protein corresponding to a concentration of 42g dm³. It consists of a single chain of 582 amino acids, globular nonglycoprotein cross-linked with 17 cystein residues (eight disulfide bonds and one free thiol) [32-34].

The studies on drug-protein binding are important in pharmacology and pharmacokinetics because drug-protein binding affects the pharmacological activities and the drug distribution [33]. The nature of interaction between the drug molecule and protein gives new opportunity for the development of new drug. Since drug is the compounds which are carried by albumin it is necessary to study the interaction of new drug with protein. The effectiveness of these compounds as pharmaceutical agents depends on their binding ability [35-37]. In addition, it is important to realize that the pharmacokinetics function of serum albumins in participating in adsorption, distribution, metabolism, and excretion of drugs and other ligands can be well-governed by rare fluctuations into a particular subset of conformational subsets, slightly different confirmations within native states [36, 37]. 

1.4 Acetylcholinesterase (AChE)  

Acetylcholinesterase (AChE) has achieved great importance in biological labeling, bioimaging and different biomedical application as optical labels [47,48]. AChE is the most important target molecule of organophosphate (OP) compound. The AChE based C-dots/ microsphere carry great importance in environmental, clinical, improved immobilization capacity for enzyme and good biocompatibility for preserving the activity of enzyme and pharmaceutical field [50]. A biomarker is designated as a substance, which is used in a normal biological process, pathogenic process, or pharmacological responses to a therapeutic intervention. The nanoparticles-biomarker interaction has implications for developing new strategies for early detection of different type diseases [7,49,50].

2.0 A Brief Review of The Work Already Done in the Field

Several researchers have focused on the interaction of nanomaterials with proteins, drugs, AChE and biomarkers from last few years. A literature survey shows that considerable efforts have been made on the interfacial, physicochemical and spectroscopic studies of drugs, in the presence and absence of proteins.  Chandra et al. [31] examined the interaction of BSA with anionic surfactant, sodium dodecyl sulphate (SDS) and cationic surfactant, cetyltrimethyl ammonium bromide (CTAB). The result shows that the better stabilizer to magnetic nanoparticles- bovine serum albumin (MNPs – BSA).

Fig. 5. Articles published on carbon dots and their applications

Shahabadi et al.[36] have carried out  the binding of a racemic mixture of antidepressant drug to BSA under the physiological condition by employing spectroscopic techniques and molecular modeling. The result of the Stern-Volmer quenching constant K_sv is inversely correlated with temperature, which indicates that, the venlafaxine (VEN)-BSA binding reaction is initiated by complex formation. The results of UV-vis spectra and CD data indicate that the conformation of BSA molecules is changed significantly in the presence of VEN.

Taboada et al. [37] analyzed the complexation process of the phenothiazine drug fluphenazine hydrochloride to HSA in aqueous buffered solutions of pH 3.0 and 7.4 with a view to elucidate the effect of hydrophobic and electrostatic forces on the complexation process and the alteration of protein conformation upon binding. It also demonstrates that at acidic pH, hydrophobic interaction between phenothiazine and protein play the predominant role in the complexation process, although the existence of electrostatic interactions is also noted.

Fig.6. Decay time distributions in the aqueous solution of HSA (0.125% w/v) and imipramine at pH 5.5 at concentrations of 0.0075 mol kg^-1

Dynamic light scattering (DLS) measurements is performed to determine the size of the protein-drug complexes Fig. 6 shows selected intensity –decay time distributions of the fluphenazine – HSA system at pH 7.4. 

Zhang et al. [38] investigated a strong interaction force between the Ractopamine (RAC) and BSA molecule showed that the drug has a long-stored time in blood plasma a profound poisonous effect. The binding site of RAC on the protein was around site I. The micro-environment and conformation of BSA was demonstrated to be changed in the presence of RAC by synchronous fluorescence spectra (SFS) and FT-IR spectra.

Bi et al. [41] suggested that tetracyclines (TTC) could bind with the serum albumins and quench the fluorescence of serum albumins. These results indicate that the technique of fluorescence quenching is a sensitive and simple way of research for the interaction of small molecules and macromolecules. The binding characteristic of biomolecules and drugs plays an important role in understanding the biological process.

Figure 7: Representative fluorescence emission spectra of HSA of different concentration of tetracycline (TTC) at room temperature.

The fluorescence spectrum of HSA at different concentration of TTC was showing Fig. 7. The results showed that the fluorescence intensity of 1.0 x 10^-5 mol l^-1 HSA and BSA solution at 340nm dropped regularly with the increasing concentration of the studied drugs and the peak shapes did not change.  The above results indicate that there were interaction between the drugs and HSA or BSA and the binding action produced the non-fluorescent complexes.

Choudhary et al. [39] observed that binding of the drugs dissolved in the pre- and post-micellar hexadecyltrimethylammonium bromide (HTAB) solutions lead to a reduction in the binding affinity of the drug in case of naproxen for the protein compared to that in the surfactant. However, in the case of diclofenac sodium, the binding affinity increases when the drug is delivered from micellar form of the surfactant.

Sulkowska et al. [40] analysed the interaction of HSA and BSA within the IIA and IIIA principal ligand-binding structural domains suggests that the binding site for the 2-mercapto-1-methylimidazole (Methimazole, MMI) and 6n-propyl-2-thiouracil (PTU) is located in subdomain IIA. Hydrophobic contacts with Leucine 203, Phenylalanine 211, electrostatic interaction of Alanine 215 with Lysine 199 and Arginine 222 towards HSA may play a key role in formation of the antithyroid drug-HSA complex.

Hage et al. [41] suggested the use of high-performance affinity chromatography (HPAC) to examine the binding of glimepiride (Scheme II), a trhird-generation sulfonylurea drug, to normal HSA and HSA with various levels of in vitro glycation. The use of HPAC in various formats allowed for a more detailed analysis of these studies to be extended to glycated HSA. This HPAC method indicated that glimepiride had a set of both high affinity sites and lower affinity regions on these proteins.

Scheme II.  Structure of glimepiride (sulfonylurea drug)

Sebille et al. [42] studied the different separation methods, the values of drug protein binding constants. The results of the binding constants measured by different separation methods are given for the albumin-phenylbutazone and albumin-warfarin systems. The results are in most cases in good agreement and prove the validity of using chromatography as a tool for measuring the binding parameters of species interacting in solution. The separation methods used to determine the drug-protein binding parameters must be selected according to the field of application.

Li et al. [43] suggested the graph theory adopted to characterize the topology information in the human protein-protein interaction (PPI) network with vertex-weighted and edge-weighted. The success of method can be attributed to two aspects. Firstly, the use of human PPI network provides us a novel viewpoint to identify potential target proteins and understand the interaction mechanisms between drugs and target proteins. Secondly, the use of graph theory provides a novel approach to study the difference of properties between target proteins and non-target proteins in the context of network.

Xiao et al. [44] examined the interaction between carbon dots (CDs) and human serum albumin (HSA). These results make better understanding of the in vitro molecular interaction between HSA and a carbon-based fluorescent nanomaterial, which is much important for the further in vivo applications of carbon, based fluorescent nanomaterials in nanomedical applications. Meng et al. [47] investigate synthesized C-dots, by using the Fentons reaction and the proposed fluorescent biosensing platform for successfully detection of the concentration of H₂O₂, choline, ACh, and the activity of choline oxidase (ChOx) and AChE.

Now a day’s depression is the most common illness in modern society and affecting approximately 15-20% of the population lifetime worldwide [51-53]. Depression is not only devasting but it will be the second largest global burden of disease, costing the United State an estimated 100 billion dollars annually [3]. Selective serotonin reuptake inhibitors (SSRIs) that act as a reuptake inhibitor by blocking the action of the serotonin transporter (SERT) at brain synapes are by far most frequently prescribed drugs for the management of depression. A well-known major drawback of current SSRIs is their slow onset of antidepressant activity requiring 3-6 weeks of treatment to produce a significant therapeutic benefit [4-6]. The use of antidepressants drugs is several side effects are dry mouth, cardiovascular effects, urinary retention and mind confusion. These factors underscore the need to elucidated alternative treatments or prevention strategies for depression. A better understanding of the interaction of TCAs with serum albumins in different conformational states and to develop more specific and subsequently, safer antidepressant. [7-9]

Recently, several new multitarget antagonists and allosteric modelators have shown improved efficacy and success in clinical trials. So, progress in faster and sustained antidepressant effect of the N-methyl-D-aspartate (NMDA) receptor antagonist, the glutamatergic system modulation has been proposed as a target for development of rational and more effective treatment to depression. In this regard, we want to determine the interaction of the most widely used TCAs including, first generation antidepressant drug amitryptiline hydrochloride (AMT), desipramine hydrochloride (DSP) and chlorpromazine hydrochloride (CPZ) with serum albumins with different conformational states. AMT, DSP and CPZ have structurally constituted of small hydrocarbon chain with a terminal nitrogen atom and planar tricyclic ring system. The chemical substituents in the molecular structure of antidepressant molecules, amitriptyline, desipramine and chlorpromazine hydrochlorides are structurally related antidepressants whose only difference is the existence of an extra methyl group in the hydrophobic side chain of chlorpromazine instead of a sulfur atom if compared with desipramine [-51,52,6,8].

The binding mechanism of proteins with ligands from last few years shed light on different areas of research and its important applications in diverse fields of science as the development of new biomaterials, biochemistry, food chemistry or pharmaceutical sciences. The nature of interaction between the drug molecule and protein gives new opportunity for the development of new drug. Since drugs are the compounds which are carried by albumin it is necessary to study the interaction of new drug with protein. [53-55]. The result of this study shows the technique of fluorescence quenching is sensitive and simple way to understand the interactions of small molecules and macromolecules. The information of the interaction between drugs and serum albumins or drug and nucleic acid, etc. will help to design a wide variety of new drug [56,57].

3.0 Conclusion

The exploration of carbon dots (CDs) as nanocarriers and bio-interactive platforms has opened new avenues in biomedical research. This review highlights the multifaceted interactions between CDs and key biological targets, including serum albumins (BSA and HSA), antidepressant drugs, and the acetylcholinesterase (AChE) enzyme. CDs exhibit excellent biocompatibility, tunable surface functionalities, and strong fluorescence properties, making them ideal candidates for drug delivery, bioimaging, and biosensing applications. Their interactions with serum albumins suggest potential for efficient drug transport and controlled release, while binding studies with antidepressant drugs indicate that CDs can enhance drug solubility and stability without compromising therapeutic efficacy. Furthermore, the ability of CDs to modulate AChE activity introduces new possibilities in the treatment and diagnosis of neurodegenerative disorders such as Alzheimer’s disease.Overall, the bioconjugation of CDs with therapeutic molecules and biomacromolecules provides a promising platform for advancing nanomedicine. Future research should focus on in vivo evaluations, long-term toxicity assessments, and the development of CD-based multifunctional systems for targeted and responsive therapeutic interventions.

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