Nanoscale aggregates onto ultrathin films are gaining importance due to their potential applications towards opto-electronic device application.
Recently we have developed a series of aggregates (J aggregate/H aggregate/excimer etc) onto thin films via LB/LbL techniques. See list of publications: click here
Fluorescence Resonance Energy Transfer (FRET):
FRET is a physical dipole–dipole coupling between the excited state of a donor fluorophore and an acceptor chromophore that causes relaxation of the donor to a non-fluorescent ground state, which excites fluorescence in the acceptor. In the process of FRET, initially a donor fluorophore (D) absorbs the energy due to the excitation of incident radiation and transfers the excitation energy to a nearby chromophore, the acceptor (A). The process can be expressed as follows:
FRET is a highly distance dependent phenomenon – 1 to 10 nm distance between donor and acceptor flurophore is crucial for the process to occur. There are few criteria that must be satisfied in order for FRET to occur.
(a) the fluorescence spectrum of the donor molecule must overlap with the absorption or excitation spectrum of the acceptor chromophore. The degree of overlap is referred to as spectral overlap integral.
(b) The two fluorophores (donor and acceptor) must be in the close proximity to one another (typically 1 to 10 nanometer).
(c) The transition dipole orientations of the donor and acceptor must be approximately parallel to each other.
(d) The fluorescence lifetime of the donor molecule must be of sufficient duration to allow the FRET to occur.
FRET has wide applications in biomedical, protein folding, RNA/DNA identification, sensors, investigating molecular level interactions etc.
Recently we have developed several FRET based sensors – Hard water sensor (link 1), Ion sensor (link 1), pH sensor (link 1, link 2), DNA sensor (link 1 link 2 link 3), Cholesterol sensor, Arsenic sensor etc. See the publication list. click here.
Download review paper written by me:
1. Fluorescence Resonance Energy Transfer (FRET) sensor (Invited Review article) download pdf
2. Nano Dimensional Hybrid Organo-clay Langmuir-Blodgett Films (Invited review article) download pdf
Introduction to Molecular Engineering:
Molecular materials are currently used in many different applications, from plastics for new building materials to light emitting diodes.
My current research activities include the preparation and characterizations thin films of some interesting organic, inorganic, metallorganic, dyes and biomolecules and organo-clay hybrid films. Also to explore the organization and molecular mechanism involves in such systems.
In order to fabricate a thin film of the material under investigations are deposited onto solid substrate. This can be accomplished in a variety of ways, however we use mainly spincoating, Layer-by-Layer (LbL) self assembly, and Langmuir-Blodgett (LB) deposition technique. Although we are particularly interested in the Langmuir-Blodgett technique, which allows organic structures to be assembled sequentially, one molecular monolayer at a time. The resultant film thickness can therefore be precisely controlled. In addition, the orientation of the molecules within the films can be arranged so that the multilayered structure possesses specific functional characteristics.
The aim of these work is to identify structure-property relationships within such thin films and investigate the mechanisms through which certain physical or chemical processes occur.
Langmuir-Blodgett films have long formed the core of our research activity; however, we rarely delve into the area of ideal LB compatible materials in which classically amphiphilic molecules ensure highly ordered molecular arrangement. Instead, we prefer to push the LB technique to new limits, investigating a much broader range of material types. For instance our current work involves investigations of non-amphiphilic molecules, water soluble materials, organo-clay hybrid materials and biomolecules (DNA, lipid, RNA) into the restricted geometry indicating that our approach to research is based on being diverse rather than too narrow.
Clay particles are natural nanoparticles with cation exchange capacities and have layered structure. Due to strong cation exchange capacity (CEC) or intercalation properties of clay the organic molecules are either adsorbed on to the clay surface or enter in to the inter laminar space of clay surface resulting the formation of organo-clay hybrid system. It is possible to prepare ultrathin films of organo-clay hybrids by LB or LbL technique. In this hybrid system the organic part gives the flexibility whereas the inorganic part imparts the stability. Interesting new properties are observed in such systems energy transfer, nonlinear optics, nano-aggregates, J-dimer etc.
References: Click here to read my publication
A short animation showing how langmuir blodgett coating works
The history of Molecular Monolayer: