Engineering the Nanoparticle Surface for Protein Recognition and Applications

Proteins and nanoparticles (NPs) provide a promising platform for supramolecular interaction. We are currently exploring both fundamental and applied aspects of this interaction. On the fundamental side, we have fabricated a series of water-soluble anionic and cationic NPs to interact with cationic and anionic proteins respectively. A Varity of studies such as, activity assay, fluorescence titration, isothermal titration calorimetry etc. were carried out to quantify the binding properties of these functional NPs with those proteins. Those studies reveal the prospect of tuning the affinity between the nanoparticles and proteins by the surface modification. On the application side, we have used this protein-nanoparticle interaction in protein refolding where we successfully refolded the thermally denatured proteins toward its native structure. We have also applied this particle-protein recognition to create a biocompatible protein sensor using a protein-NP conjugate. Green fluorescent protein and a series of cationic NPs were used for a protein sensor for the identification of protein analytes through displacement process. We have extended this application even in sensing the proteins in human serum

Nano-Graphene Oxide Based Multichannel Sensor Arrays towards Sensing of Protein Mixtures

Optical array-based sensors are attractive candidates for the detection of various bio-analytes due to their convenient fabrication and measurements. For array-based sensors, multichannel arrays are more advantageous and used frequently in many electronic sensors. But most reported optically array based sensors are constructed on a single channel array. This difficulty is mainly instigated from the overlap in optical responses. In this report we have used nano-graphene oxide (nGO) and suitable fluorophores as sensor elements to construct a multichannel sensor array for the detection of protein analytes. By using the optimized multichannel array we are able to detect different proteins and mixtures of proteins with 100 % classification accuracy at sub-nanomolar concentration. This modified method expedites the sensing analysis as well as minimizes the use of both analyte and sensor elements in array-based protein sensing. We have also used this system for the single channel array-based sensing to compare the sensitivity and the efficacy of these two systems for other applications. This work demonstrated an intrinsic trade-off associated with these two methods which may be necessary to balance for array-based analyte detections

Empirical Correlation and Validation of Lateral Size-Dependent Absorption Coefficient of Graphene Oxides

For various applications of graphene oxide (GO), fast and accurate concentration determination of a GO solution is highly important and plays a very crucial role in many applications. One of the most convenient method to determine concentration of an unknown solution is by using absorption coefficient of the specific material by using UV-Vis absorption spectroscopy. In this study we have determined the absorption coefficient of various GO solutions with average lateral size distribution from 40 nm to 7760 nm and successfully able to correlate them. The absorption coefficient of those samples were measured at 660 nm using UV-Vis absorption spectroscopy. A linear relationship between the logarithm of absorption coefficient and average lateral diameter was observed by considering values from both AFM and DLS analysis. The empirical relation was further validated by estimating the concentration of unknown GO solutions and applied them in study of GO mediated enzymatic inhibition. Hence this calibrated relationship can be used in a very convenient way for concentration or average size determination of an unknown GO solution

Interaction of Amino Acids and Graphene Oxide: Trends in Thermodynamic Properties

Recent studies on interaction of graphene oxide with proteins and peptides has attracted a lot of attention in biomedical applications. Hence, fundamental and experimental estimation of binding thermodynamics between various amino acids and graphene oxide is highly significant for many aspects. In this study, the interaction of graphene oxide (GO) with amino acids bearing variable charge, hydrophobicity, and aromatic moieties are studied by using isothermal titration calorimetry. To explore the effect of lateral size and degree of oxidation in GO, we employ two different sizes of GO. The results show that the interactions of GO with amino acids are mainly governed by electrostatic and π–π interaction with variable enthalpy and entropy values. The highest complex stability is observed in the case of tryptophan and arginine followed by other amino acids containing either positive charge or aromatic moieties. Amino acids bearing other functional groups either exhibit very weak interaction or did not show any detectable binding. This trend and origin of interaction is further confirmed by zeta potential (for cationic amino acids) and fluorescence titration assay (for aromatic amino acids). Furthermore, there is a significant enthalpy–entropy correlation between GO and amino acids that is observed with near unit slope (α = 0.87) and positive intercept (<i>T</i>Δ<i>S</i>₀ = 18.65). This indicates the flexible nature of GO as a receptor against small molecules. In the future, this investigation will help in designing the peptide-based receptors for GO and understanding the nature of the interaction of proteins and peptides with GO-based receptors

Simultaneous Exfoliation and Functionalization of 2H-MoS2 by Thiolated Surfactants: Applications in Enhanced Antibacterial Activity

Two-dimensional transition metal dichalcogenides (TMDs), such as MoS2, generally exist in two different polymorphic structures, metallic (1T phase) and semiconducting (2H phase). In context of their wide spectrum of applications ranging from electronic to biomedicine, the aspects of ligand conjugation and solution processability are highly significant. In addition, the assessment of their antibacterial property and biocompatibility is equally important to explore their biomedical applications. Here we report a new method for the exfoliation and direct functionalization of 2H-MoS2 using surfactant molecules with thiol functionality. We found that the exfoliated MoS2 using thiolated ligands are functionalized with desired functionality and the processing scheme can be extended to other TMDs. Functionalized 2H-MoS2 exhibits highly enhanced antibacterial efficiency compared to similarly functionalized metallic 1T-MoS2 against pathogenic bacteria. The newly synthesized functionalized 2H-MoS2 exhibits better hemocompatibility, which makes it suitable for in vivo applications. This convenient functionalization method opens the door for many other applications of functionalized semiconducting 2H-MoS2 and other TMDs

Diastereo- and Enantioselective Synthesis of Highly Functionalized Tetrahydropyridines by Recyclable Novel Bifunctional <i>C</i>₂-Symmetric Ionic Liquid–Supported (<i>S</i>)-Proline Organocatalyst

An efficient, novel bifunctional C2-symmetric ionic liquid–supported (S)-proline organocatalyst 7 was developed for a one-pot, five-component reaction involving β-keto esters 8, aryl aldehydes 9, and aryl amines 10, affording highly functionalized tetrahydropyridines 11a–o by simultaneous generation of fives bonds and two stereogenic centers with extraordinary diastereo- and enantioselectivities (up to >99:1 dr, 95:5 er) in isopropanol with high yields (up to 92%). This protocol provides quick access to diverse enantio-enriched, highly functionalized diastereo- and enantioselective tetrahydropyridines in a green medium without any column chromatographic purification. The catalyst was recycled five times without significant loss of its catalytic activity

Biomimetic Interactions of Proteins with Functionalized Nanoparticles: A Thermodynamic Study

Gold nanoparticles (NPs) functionalized with L-amino acid-terminated monolayers provide an effective platform for the recognition of protein surfaces. Isothermal titration calorimetry (ITC) was used to quantify the binding thermodynamics of these functional NPs with alpha-chymotrypsin (ChT), histone, and cytochrome c (CytC). The enthalpy and entropy changes for the complex formation depend upon the nanoparticle structure and the surface characteristics of the proteins, e.g., distributions of charged and hydrophobic residues on the surface. Enthalpy-entropy compensation studies on these NP-protein systems indicate an excellent linear correlation between DeltaH and TDeltaS with a slope (alpha) of 1.07 and an intercept (TDeltaS0) of 35.2 kJ mol(-1). This behavior is closer to those of native protein-protein systems (alpha = 0.92 and TDeltaS0 = 41.1 kJ mol(-1)) than other protein-ligand and synthetic host-guest systems

Graphene Oxide as a Carbocatalyst for a Diels-Alder Reaction in an Aqueous Medium

The Diels-Alder (DA) reaction, a 4+2] cycloaddition reaction, is highly important in synthetic organic chemistry and is frequently used in the synthesis of natural products containing six-membered rings. Herein, we report an efficient protocol for the DA reaction between 9-hydroxymethylanthracene and N-substituted maleimides using two-dimensional graphene oxide (GO) as a heterogeneous carbocatalyst in an aqueous medium at room temperature. High yields, a wide substrate scope, low temperature, excellent functional group tolerance, atom economy, and water as a green solvent are noteworthy features of this protocol. The heterogeneous GO catalyst can be easily recovered and used multiple times without any significant loss in catalytic activity

Removal of reactive dyes using a high throughput-hybrid separation process

Toxic and carcinogenic reactive dyes are abundantly used in textile industries due to their wide variety of colour and texture. In this study, a hybrid separation process was used to remove four common reactive dyes (reactive yellow, red, black and brown) from aqueous solution. Synthetic solution of these dyes was subjected to adsorption by activated carbon followed by microfiltration (MF), using a ceramic membrane module. Dyes were completely removed by adsorption at pH 4.5 and the dye-loaded adsorbents were removed by cross-flow MF. Maximum Langmuir adsorption capacity of activated carbon for these four dyes was in the range of 88-106mg/g. Effects of trans-membrane pressure drop and cross-flow rate on the throughput of the combined process was investigated. Membrane fouling was due to the cake type of layer formed by the activated carbon particles. Five different washing protocols were tested for their efficiency and the acid-alkali wash was found to be the most effective