PONDICHERRY UNIVERSITY

CENTRE FOR NANOSCIENCE AND TECHNOLOGY

NANOPHOTONICS AND BIOPHOTONICS

TOPIC :Metallic nanoparticles and nanorods for Biosensing      

SUBMITTED TO                                                                               SUBMITED BYDR P. THANGADURAI                                                             VENKATA KISHORE .PERLA

                                                                                                       M.TECH  II YEAR

What is a Biosensor?

Nanotechnology opened doors to new ways of identifying and quantifying biomolecules through use of nanosensors and nanoprobes.

• Tools are capable of monitoring biomolecular processes within single cells.

• Use in biological and medicinal research.

• Two major categories,

(i) biosensors (consists of biological recognition element called bioreceptor (Ab, NA or enzyme, cell) and a signal transducer

(ii) chemical sensors (chemical recognition element eg pH sensitive dye and a signal transducer).

Nano sensors

Why Nanosensors ???

Particles that are smaller than the characteristic lengths associated with the specific phenomena often display new chemistry and new physics that lead to new properties that depend on size

When the size of the structure is decreased, surface to volume ratio increases considerably and the surface phenomena predominate over the chemistry and physics in the bulk

The reduction in the size of the sensing part and/or the transducer in a sensor is important in order to better miniaturise the devices

Science of nano materials deals with new phenomena, and new sensor devices are being built that take advantage of these phenomena

Sensitivity can increase due to better conduction properties, the limits of detection can be lower, very small quantities of samples can be analysed, direct detection is possible without using labels, and some reagents can be eliminated.

Why metal nano particles as sensors

• The unique optical and electromagnetic properties of metal nanoparticles can be utilized in several areas including biosensing.

• The plasmonic resonance created in metal nanoparticles is extremely sensitive for changes in their surroundings, making them suitable elements for sensing applications.

Nobel metal nano particles

• In particular, the unique properties of noble metal nanoparticles have allowed for the development of new biosensing platforms with enhanced capabilities in the specific detection of bioanalytes.

• Noble metal nanoparticles show unique physicochemical properties (such as ease of functionalization via simple chemistry and high surface-to-volume ratios) that allied with their unique spectral and optical properties have prompted the development of a plethora of biosensing platforms.

• Several researchers have focused on biosensor for monitoring of biological interaction. Moreover, the detection of bimolecular is an extremely significant problem. Hence, the development of optical biosensors based on optical properties of noble metal nanoparticles using Surface Plasmon Resonance was considered.

• Surface plasmon resonance (SPR) is a powerful technique to retrieve information on optical properties of biomaterial and nanomaterials. Biosensor based on SPR is a versatile technique for biological analysis applications. Essentially, SPR depends on the optical properties of metal layer and enviromental changes so it is related to charge density oscillation at the interface between them .

• One advantage of SPR is, the light beam never passes through the dielectric medium of interest and hence the effect of absorption of the light in the analyte can be ignored. Hence, the main potential of surface plasmon resonance is characterization of medium after the metal layer.

• Biomolecular interaction are determined and predicted via angular modulation sensor; hence, the out put of SPR biosensor sensor is angle shift (θspr), associated with the point of minimum reflected light intensity and is very sensitive to the changes in the dielectric constant of the medium.

• Fundamentally, the base of the biosensor is the coupling of a ligand-receptor binding reaction to a signal transducer. Moreover, angular, phase and polarization modulations are the various methods applicable for distinguishing the interaction of bimolecular with the receptor.

• Essentially, SPR is a quantum electromagnetic phenomenon that appears at the interface of the dielectric and the metal. Under certain conditions, the energy of the light beam is absorbed by collective excitation of the free electrons called surface Plasmon (SP), which lies between the interface of the dielectric and the metal.

• On the other hand, when the momentum of the photon matches that of the Plasmon, the resonance appears as an interface of two two media with dielectric constants of opposite signs, and the SP wave propagates along the interface. In accordance with the SP wave properties, the SPR is classified as propagating the SPR, the long-range SPR and the localized SPR.

METAL NANO RODS FOR BIOSENSOR

A general setup for thermal-vapor transport method

Synthesis of metal nano rodsThermo-vapor transport method

Catalyst-assisted fabricationDeposition of a catalyst layer, e.g. thermal evaporation of a 10 nm thick metal filmor injection of a precursor which decomposes into particles

ZnO nanorods on Au and NiO catalysts

Template-based Methods

Kim k. et al.

A schematic summary of the kinds of quasi-one-dimensional metaloxide nanostructures

(A) nanowires and nanorods; (B) core-shell structures with metallic inner core, semiconductor, or metal-oxide; (C) nanotubules/nanopipes and hollow nanorods; (D) heterostructures; (E) nanobelts/nanoribbons; (F) nanotapes, (G) dendrites, (H) hierarchical nanostructures; (I) nanosphere assembly; (J) nanosprings.

• Gold nanoparticles have a long history as optical or electron microscopy labels. More recently, their plasmon resonance has been employed for more elaborate optical nanoscopic-sensing schemes.

• Rod-shaped nano-particles remain popular for plasmonic applications. Some reasons for this are the ability to fabricate gold nanorods in high quality using seeded crystallization from solution, the adjustability of the plasmon resonance by varying the aspect ratio, the strong scattering efficiency, and the low plasmon damping in nanorods

• There are several different quantities that describe the performance of a plasmonic structure for sensing applications on a single particle level—and all of them have their merits for certain applications. We will discuss the most important of them in the following Paragraphs — the plasmonic sensitivity to refractive index change as well as various ‘figures of merit’—and present their dependency on nanorods

• In practice, one would normally detect a spectral shift of a resonance as a relative intensity change dl/l at a fixed wavelength λ0induced by a small index change dn. We can therefore define an alternative dimensionless figure of merit:

• Bio-sensing applications are even more complex. In this case, one seeks to detect the binding of small (organic) molecules to the nanoparticle surface instead of exchanging the entire embedding medium. The spectral shift now depends on the relative size of the molecules to the volume the plasmon field penetrates into the medium.

• Furthermore, the sensitivity is reduced with increasing distance to the particles surface. A‘figure of merit’ trying to capture the different sensing volumes of various nanostructures can be defined as the FOM layer * for a homogeneous coating of molecules with a specific refractive index (for example, n=1.5, typical for organic molecules) in a layer of thickness l around the particle normalized to this layer thickness. The formal definition of this ‘ figure of merit for thin layers’FOM layer*is therefore

References 

• The Optimal Aspect Ratio of Gold Nanorods for Plasmonic Bio-sensing.

• BIOSENSOR  by Pier Andrea Serra Intech.• Application of Surface Plasmon Resonance 

Based on a Metal Nanoparticle.• http://dx.doi.org/10.5772/512191.

Than

k you