Detection of base-pair mismatches in DNA using graphene-based nanopore device.

We present a unique way to detect base-pair mismatches in DNA, leading to a different epigenetic disorder by the method of nanopore sequencing. Based on a tight-binding formulation of a graphene-based nanopore device, using the Green's function approach we study the changes in the electronic transport properties of the device as we translocate a double-stranded DNA through the nanopore embedded in a zigzag graphene nanoribbon. In the present work we are not only successful in detecting the usual AT and GC pairs but also a set of possible mismatches in the complementary base pairing.

Localization phenomena in a DNA double-helix structure: a twisted ladder model.

In this work we propose a model for the DNA double helix within the tight-binding framework that incorporates the helicity of the molecules. We have studied the localization properties of three DNA sequences, the periodic poly(dG)-poly(dC) and poly(dA)-poly(dT) sequences and the random ATGC sequence (where A is adenine, T is thymine, G is guanine, and C is cytosine), all of which are coupled to the backbone with random site energies representing the environmental fluctuations. We observe that due to the helicity of DNA, electron transport is greatly enhanced and there exists an almost disorder-strength-independent critical value of the hopping integral, which accounts for the helicity of DNA, for which the electronic states become maximally extended. We have also investigated the effect of backbone energetics on the transmission and I-V characteristics of DNA.

Effect of external electric field on the charge density waves in one-dimensional Hubbard superlattices.

We have studied the ground state of one-dimensional Hubbard superlattice structures with different unit-cell sizes in the presence of an electric field. A self-consistent Hartree-Fock approximation calculation is done in the weak- to intermediate-interaction regime. Studying the charge gap at the Fermi level and the charge density structure factor, we get an idea of how the charge modulation on the superlattice is governed by the competition between the electronic correlation and the external electric field.

Increasing trend of HIV seropositivity in a sexually transmitted diseases centre and epidemiology of HIV seropositive individuals.

11,539 STD clinic attenders and 20,897 antenatal clinic (ANC) attenders at a New Delhi hospital were screened for HIV antibodies by ELISA over a 3-year period. Results were confirmed by Western Blot. A low HIV seropositivity rate (1 per 1000) with an increasing trend in 1993 (4 per 1000) was observed in the STD attenders as against 0.1 per 1000 in the normal control populations. Most of the STD attenders including all the HIV seropositives had heterosexual contact with female sex workers. Both the HIV seropositive ANC attenders acquired the infection through blood transfusion. Thirteen of 23 HIV positive STD attenders had genital lesions, 5 having ulcerative and 8 having nonulcerative STD. Their clinical presentation did not differ from the HIV negative cases but the therapeutic response in 4 was altered. None had signs of symptoms of ARC/AIDS. Two out of 6 spouses and a 2-year-old child of HIV seropositive patients were seropositive. Increasing HIV seropositivity observed in this study reflects the changing situation in the country and highlights the importance of improvement of surveillance, early diagnosis and combined approaches to the management and control of STDs and HIV.

PIP: Although India's Sexually Transmitted Diseases (STD) Control Program has been in existence for 40 years, it was not until the acquired immunodeficiency syndrome (AIDS) epidemic that a serious attempt was made to strengthen the program and collect data on conditions responsible for the spread of human immunodeficiency virus (HIV). In this study, 11,539 individuals attending the Regional STD Teaching, Training, and Research Center in New Delhi during a 3-year period and 20,897 antenatal clinic patients at a New Delhi hospital were screened for HIV. The overall HIV seropositivity rate was 2.0/1000 among STD clinic attenders, but there was an increase from 1.0/1000 in 1990 to 4.1/1000 in 1993. The overall rate for antenatal patients was 0.1/1000. Heterosexual transmission, largely through contact with commercial sex workers, was the source of HIV transmission in almost half of the 23 infected STD clients. The 2 HIV-1 cases involving pregnant women were acquired through blood transfusion. 13 of the HIV-infected STD clients had genital lesions and, in 4 of these cases, the response to treatment was compromised (i.e., no response or a slow response). Two out of 6 spouses and a 2-year-old child of HIV-infected subjects were also seropositive. Although the incidence of HIV was small in this New Delhi study, increasing interactions with Bombay, where HIV incidence is at 35% of commercial sex workers, may change this situation.