Gold Nanoparticle‐Based Redox Signal Enhancement for Sensitive Detection of Human Chorionic Gonadotropin Hormone

A sensitive immunosensor for the detection of pregnancy marker, human chorionic gonadotropin hormone (hCG), was developed using the direct electrical detection of Au nanoparticles. We utilized disposable screen‐printed carbon strips (SPCSs) for the development of our immunosensor, which provided cost‐effective tests with the required antigen sample volume as small as 2 μL. After the recognition reaction between the surface‐immobilized primary antibody and hCG, the captured antigen was sandwiched with a secondary antibody that was labeled with Au nanoparticles. Au nanoparticles were exposed to a preoxidation process at 1.2 V for 40 s, which was subsequently followed with a reduction scan on the same surface using differential pulse voltammetry (DPV). We could observe Au nanoparticle‐labeled antigen‐antibody complexes immobilized on the surface of SPCS using scanning electron microscopy (SEM). Additionally, the number of Au nanoparticles on the immunosensor was determined using SEM images, and showed a linear relationship with the current intensity obtained from the DPV measurements with a detection limit of 36 pg/mL hCG (612 fM, 3.6×10^?4 IU/mL). Our immunosensor system, a combination of the screen‐printing technology with Au nanoparticles provides a promising biosensor for various applications in life sciences.     

New obstructions to symplectic embeddings

In this paper we establish new restrictions on the symplectic embeddings of basic shapes in symplectic vector spaces. By refining an embedding technique due to Guth, we also show that they are sharp.     

Miniaturized Electrochemical Immunosensor for Label‐Free Detection of Growth Hormone

A miniaturized immunosensor was developed in connection with disposable screen‐printed carbon strips (SPCS) for the point‐of‐care detection of growth hormone. The performance of the miniaturized system was studied using growth hormone (GH) as the target protein and compared with a conventional electrochemical analyzer. The detection limit of 25 pg/mL was observed for GH in 20 µL sample volume, which indicated that this versatile platform can be easily adapted for decentralized electrochemical immunosensing of clinically important proteins.     

A new algorithm for approximating the least concave majorant

The least concave majorant, \(\hat F\), of a continuous function F on a closed interval, I, is defined by

$$\hat F\left( x \right) = \inf \left\{ {G\left( x \right):G \geqslant F,Gconcave} \right\},x \in I.$$

We present an algorithm, in the spirit of the Jarvis March, to approximate the least concave majorant of a differentiable piecewise polynomial function of degree at most three on I. Given any function F ∈ C⁴(I), it can be well-approximated on I by a clamped cubic spline S. We show that \(\hat S\) is then a good approximation to \(\hat F\).

We give two examples, one to illustrate, the other to apply our algorithm.     

Ultrasonic study of molecular interaction in binary liquid mixtures at 30°C

Densities ρ and ultrasonic speeds u of the binary mixtures of tetrahydrofuran (THF) with 1-butanol and tert-butanol, at 30°C, over the entire composition range were measured. From these data isentropic compressibility, K _s, intermolecular free length L _f, relative association R _A, acoustic impedance Z, molar sound speed R _m, deviations in isentropic compressibility ΔK _s, and excess volume V ^E were calculated. The variation of these parameters with composition of the mixture helps us in understanding the nature and extent of interaction between unlike molecules in the mixtures. Further, theoretical values of ultrasonic speed were evaluated using theories and empirical relations. The relative merits of these theories and relations were discussed.     

Rheology of semi-dilute solutions of calf-thymus DNA

We study the rheology of semi-dilute solutions of the sodium salt of calf-thymus DNA in the linear and nonlinear regimes. The frequency response data can be fitted very well to the hybrid model with two dominant relaxation times τ₀ and τ₁. The ratio (τ₀/τ₁) ∼5 is seen to be fairly constant on changing the temperature from 20 to 30°C. The shear rate dependence of viscosity can be fitted to the Carreau model.     

DOSY technique applied to palladium nanoparticles in ionic liquids

Multinuclear ((1)H, (31)P, (19)F and (11)B) diffusion ordered spectroscopy (DOSY) technique has been applied to palladium nanoparticles systems dispersed in ionic liquids (ILs). Even if the nanoparticles themselves cannot be detected through NMR, observation of the solvent (methanol) and the IL ([BMI][PF(6)] or [BMI][NTf(2)]), their diffusion coefficients and their changes in the presence of nanoparticles allow us to draw significant assumptions about the organisation of palladium nanoparticles in the IL. For comparison, the corresponding molecular precursors ([PdCl(2)(cod)] or [Pd(2)(dba)(3)]) have been also studied.     

Amyloid-beta detection with saccharide immobilized gold nanoparticle on carbon electrode

The electrochemical sensing of saccharide-protein interactions using a couple of sialic acid derivatives and Alzheimer's amyloid-beta (Abeta) is described. The densely-packed saccharide area for recognition of protein was fabricated onto a carbon electrode by three steps, which were electrochemical deposition of Au nanoparticles on a screen printed strip, self-assembled monolayer (SAM) formation of the acetylenyl group on Au nanoparticles, and the cycloaddition reaction of an azide-terminated sialic acid to the acetylenyl group. The attachment of Abeta peptides to the sialic acid layer was confirmed by electrochemistry and atomic force microscopy imaging. The intrinsic oxidation signal of the captured Abeta(1-40) and (1-42) peptides, containing a single tyrosine (Tyr) residues, was monitored at a peak potential of 0.6 V (vs Ag/AgCl within this sensor) in connection with differential pulse voltammetry. The peak current intensities were concentration dependent. The proposed process provides new routes for analysis of saccharide-protein interactions and electrochemical biosensor development.     

Coherent decay of Bose-Einstein condensates

Atomic Bose-Einstein condensates are singular forms of matter with the coherence between constituent atoms as a defining characteristic. Although this viewpoint is increasingly validated through experimental findings, the mechanisms behind the observed losses are still understood with classical recombinant collision arguments between particles within the condensate itself. By incorporating a general interparticle interaction into the Hamiltonian, a coherent decay rate can be obtained, thus providing a direct link between the observed losses and the microscopic two-body parameters. Appearing in the lifetime, the interaction strength, lambda, is expressed as lambda=8 pia/(1-delta), where the small parameter delta is obtained from a fit to experimental loss data. Most importantly, the lowest order rate exhibits a novel density dependence (rho{3/2}) that can be identified in low temperature tests.     

Voltammetric determination of isoproterenol using a 5-amino-2’,4’-dimethoxybiphenyl-2-ol modified carbon nanotube paste electrode

A new electrochemical sensor for determination of isoproterenol(IP) is described.The sensor is based on carbon paste electrode (CPE) modified with 5-amino-2’,4’-dimethoxybiphenyl-2-ol(5ADMB) and takes the advantages of carbon nanotubes(CNTs). Under the optimum pH of 7.0,the oxidation of IP occurs at a potential about 210 mV less positive than that of the unmodified CPE. The oxidation currents increased linearly with two concentration intervals of IP,one is 0.09 to 20.0 |xmol/L and,the other is 20.0 to 400.0μmol/L.The detection limit(3σ) obtained by square wave voltammetry(SWV) was 39.0 nmol/L.The practical application of the modified electrode was demonstrated by determining IP in IP ampoule,urine and human blood serum samples.