Advanced electrocatalytic materials based biosensors for cancer cell detection – A review

Herein, we have highlighted the latest developments on biosensors for cancer cell detection. Electrochemical (EC) biosensors offer several advantages such as high sensitivity, selectivity, rapid analysis, portability, low-cost, etc. Generally, biosensors could be classified into other basic categories such as immunosensors, aptasensors, cytosensors, electrochemiluminescence (ECL), and photo-electrochemical (PEC) sensors. The significance of the EC biosensors is that they could detect several biomolecules in human body including cholesterol, glucose, lactate, uric acid, DNA, blood ketones, hemoglobin, and others. Recently, various EC biosensors have been developed by using electrocatalytic materials such as silver sulfide (Ag₂S), black phosphene (BPene), hexagonal carbon nitrogen tube (HCNT), carbon dots (CDs)/cobalt oxy-hydroxide (CoOOH), cuprous oxide (Cu₂O), polymer dots (PDs), manganese oxide (MnO₂), graphene derivatives, and gold nanoparticles (Au-NPs). In some cases, these newly developed biosensors could be able to detect cancer cells with a limit of detection (LOD) of 1 cell/mL. In addition, many remaining challenges have to be addressed and validated by testing more real samples and confirm that these EC biosensors are more accurate and reliable to measure cancer cells in the blood and salivary samples.     

o-Cresol,thiourea and formaldehyde terpolymer – A cation exchange resin

o-Cresol–thiourea–formaldehyde terpolymer resin was synthesized through the condensation of o-cresol and thiourea with formaldehyde in the mole ratio 1:3:5 in the presence of 2 M hydrochloric acid as a catalyst. The resulting copolymer was characterized with IR and ¹H NMR spectral data. The average molecular weight of the resin was determined by Gel permeation chromatography. Thermal study of the resin was carried out to calculate the activation energy (Ea), enthalpy of activation (H³), entropy of activation (S³), free energy of activation (G³), and pre-exponential factor (A) of various steps of thermal decomposition of the terpolymer. The Dharwadkar and Kharkhanavala method has been used to calculate thermal activation energy and thermal stability. The chelation ion-exchange properties were also studied with the batch equilibrium method. The chelation ion-exchange properties of the copolymer was studied for Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺ and Cd²⁺ ions. The resin was proved to be selective chelating ion-exchange copolymer for certain metals. The study was carried out over a wide pH range and in media of various ionic strengths.     

Equilibrium, kinetics, mechanism, and process design for the sorption of methylene blue onto rice husk

Batch experiments were carried out for the sorption of methylene blue onto rice husk particles. The operating variables studied were initial solution pH, initial dye concentration, adsorbent concentration, and contact time. Equilibrium data were fitted to the Freundlich and Langmuir isotherm equations and the equilibrium data were found to be well represented by the Langmuir isotherm equation. The monolayer sorption capacity of rice husks for methylene blue sorption was found to be 40.5833 mg/g at room temperature (32 degrees C). The sorption was analyzed using pseudo-first-order and pseudo-second-order kinetic models and the sorption kinetics was found to follow a pseudo-second-order kinetic model. Also the applicability of pseudo second order in modeling the kinetic data was also discussed. The sorption process was found to be controlled by both surface and pore diffusion with surface diffusion at the earlier stages followed by pore diffusion at the later stages. The average external mass transfer coefficient and intraparticle diffusion coefficient was found to be 0.01133 min(-1) and 0.695358 mg/g min0.5. Analysis of sorption data using a Boyd plot confirms that external mass transfer is the rate limiting step in the sorption process. The effective diffusion coefficient, Di was calculated using the Boyd constant and was found to be 5.05 x 10(-04) cm2/s for an initial dye concentration of 50 mg/L. A single-stage batch-adsorber design of the adsorption of methylene blue onto rice husk has been studied based on the Langmuir isotherm equation.     

A site energy distribution function from Toth isotherm for adsorption of gases on heterogeneous surfaces

A site energy distribution function based on a condensation approximation method is proposed for gas-phase adsorption systems following the Toth isotherm. The proposed model is successfully applied to estimate the site energy distribution of three pitch-based activated carbons (PA, PFeA and PBA) developed in our laboratory and also for other common adsorbent materials for different gas molecules. According to the proposed model the site energy distribution curves of the activated carbons are found to be exponential for hydrogen at 77 K. The site energy distribution of some of the activated carbon fibers, ambersorb, Dowex optipore, 13X Zeolite for different adsorbate molecules represents a quasi-Gaussian curve with a widened left hand side, indicating that most sites have adsorption energies lower than a statistical mean value.     

Athermal simulation of plastic deformation in amorphous solids at constant pressure

An algorithm is introduced for the molecular simulation of constant-pressure plastic deformation in amorphous solids at zero temperature. This allows to directly study the volume changes associated with plastic deformation (dilatancy) in glassy solids. In particular, the dilatancy of polymer glasses is an important aspect of their mechanical behavior. The new method is closely related to Berendsen's barostat, which is widely used for molecular dynamics simulations at constant pressure. The new algorithm is applied to plane strain compression of a binary Lennard-Jones glass. Conditions of constant volume lead to an increase of pressure with strain, and to a concommitant increase in shear stress. At constant (zero) pressure, by contrast, the shear stress remains constant up to the largest strains investigated (ε = 1), while the system density decreases linearly with strain. The linearity of this decrease suggests that each elementary shear relaxation event brings about an increase in volume which is proportional to the amount of shear. In contrast to the stress–strain behavior, the strain-induced structural relaxation, as measured by the self-part of the intermediate structure factor, was found to be the same in both cases. This suggests that the energy barriers that must be overcome for their nucleation continually grow in the case of constant-volume deformation, but remain the same if the deformation is carried out at constant pressure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2057–2065, 2004     

Subordination and superordination results associated with the generalized hypergeometric function

In the present investigation, we obtain some subordination and superordination results involving Hadamard products for certain normalized analytic functions in the open unit disk. Relevant connections of the results, which are presented in this paper, with various other known results are also pointed out.     

Protein–Nucleic acid interactions: Investigations on the peptide backbone interaction with polynucleotides

Model building, difference spectroscopy, and ¹H and ¹³C NMR experiments have been carried out to study the binding of poly(L -Ser) with the polyribonucleotides poly(A) and poly(U) at pH 7.1. Studies have also been carried out with base paired duplexes poly(A)?poly(U). Peak doubling of C^α and carbonyl resonances in the ¹³C NMR spectrum of poly(L -Ser) in presence of polyribonucleotides is observed. From the chemical shifts and the linewidth, it is concluded that the interaction occurs through hydrogen bonding between the nucleic acid bases and the peptide backbone. In case of poly(A) and poly(U) the hydrogen bonding scheme with peptide backbone is different from that in the base paired poly(A)?poly(U). The possible binding schemes of double stranded DNA and peptide backbone have been investigated using model building and potential energy calculations. The hydrogen bonding schemes discriminate between various base pairs and their sequence. It is concluded that protein backbone can play an important role in protein–nucleic acid recognition schemes.     

On the absolute stereochemistry of the photochemical rearrangement of 2,5-cyclohexadienones to lumiketones

Specification of the absolute configurations of starting material and product in the photochemical rearrangement of a 2,5-cyclohexadienone to a bicyclo[3.1.0]hexen-2-one (lumiketone) permits unambiguous determination of the stereochemistry at two crucial stages in the generally accepted reaction mechanism, namely the electrocyclic ring closure to give a 3,5-bonded intermediate, and the subsequent [1,4]-sigmatropic shift. The stereochemical course of the latter process in turn allows specification of whether the rearrangement is occurring directly from an electronically excited intermediate or a ground state zwitterion. An unconstrained monocyclic chiral cyclohexadienone has been studied in which steric constraints are minimal, and in which the system should have free choice of available pathways. The absolute configuration of the resolved dienone was determined by X-ray crystallographic analysis of a derivative containing a chiral center of known configuration. The absolute configuration of the resultant optically active diastereomeric lumiketones has been assigned from the Cotton effects observed on the corresponding dihydrolumiketones, assuming these chiroptical effects are governed by a normal Octant Rule instead of the Inverse Octant Rule which empirically correlates such data for cyclopropyl ketones lacking polarizable substituents. The limitations on these assignments are discussed, as well as alternative efforts to obtain completely unambiguous stereochemical assignments for the lumiketones. On the basis of these assignments, it is concluded that the sigmatropic shift proceeds with inversion of configuration at the migrating carbon, consistent with reaction via a ground state zwitterion.