Nano Technology In forensic science

Question 1

Nanomaterials for sensors

Answer 1

At the nanoscale, nanomaterials exhibit novel characteristics when compared to the same bulk material.

Nanomaterials used in sensors include metal nanoparticles, nanotubes, nanowires, nanofibers, nanocomposites, nanorods.

Types of nanomaterial-based sensors include optical, plasmonic, electrochemical and magnetic sensors

Nanosensors offer low limits of detection and allow for the use of very small sample volume for the analysis.

Question 2

Colloidal nanosensors

Answer 2

Noble metal NPs such as gold and silver are used.
The optical properties of these sensors change due to processes occurring to the sensor
This causes a shift in their absorption bands.
The change can be detected and quantified without sophisticated instruments.

Question 3

Plasmonic nanosensors

Answer 3

One of the properties of nanomaterials is their localized surface plasmon resonance (LSPR)

LSPR result from the collective oscillation of the free electrons on the metal surface when they are excited by an incident electromagnetic wave .

The plasmon resonance associated with noble metal nanostructures create strong electromagnetic enhancement around the nanostructure surface.

The surface plasmon shifts due to variations in the local environment of the nanomaterial.

Question 4

Surface enhanced Raman sensors

Answer 4

When the surface plasmon of a nanosensor is excited by incident light, the electromagnetic field is enhanced.
If the nanostructures on the sensor surface are closely packed (inter gaps ~10 nm), their surface plasmons couple and the electromagnetic enhancement by the incident light is very strong
These gaps are called hotspots and experience maximum electromagnetic field enhancement upon excitation of the sensor surface
When a Raman active analyte is adsorbed within the hotspots and become excited by laser light, it emits Raman signal that is greatly enhanced by the electromagnetic field of the hotspots
The analyte also form a charge transfer complex with the nanostructures of the sensor.
This facilitates the electron flow between the analyte and the nanostructures and lead to further enhancemnt

Question 5

Magnetic nanoparticle sensors

Answer 5

When functionalised nanoparticles bind to the target analyte, they cause changes in the spin - spin relaxation times of neighboring water molecules
This change can be detected by nuclear magnetic resonsnce (NMR)