Block 4 - Surface Plasmon Resonance (SPR/LSPR)

What is Surface Plasmon Resonance (SPR)?

The collective oscillation of free/conduction electrons in a metal in response to incident light at an appropriate wavelength/frequency

What occurs when SPR is produces?

Collective electron oscillation creates an enhanced electromagnetic field around the NP surface

What is the basic SPR mechanism?

Incident light → collective conduction-electron oscillation → resonance → enhanced electromagnetic field

What is localized SPR?

A plasmonic response confined/localized around a nanoscale metallic structure or NP.

What major factors can tune NP SPR?

Size, shape, coupling, composition

What is longitudinal SPR in a gold nanorod?

Electron oscillation along the length of a gold nanorod

What is transverse SPR in a gold nanorod?

Electron oscillation across the width of a gold nanorod

Why can a nanorod have multiple SPR modes?

Nanorods have asymmetric shape, where electrons can oscillate along different axes

Why is SPR useful for biosensing?

Interactions near the NP surface can change its plasmonic response, producing measurable optical changes

What can happen to SPR when NPs aggregate?

Their coupling is changed, leading to a spectral shift and measurable optical changes like color

Why is aggregation undesirable for NP synthesis?

Uncontrolled aggregation allows NPs to clump together, rather than remaining separated and colloidally stable

Why can aggregation be useful for SPR biosensing applications?

Controlled aggregation changes the plasmonic coupling, producing a measurable optical/spectral signal

What initially coats gold nanorods in the lecture DNA biosensor?

CTAB

What replaces CTAB during functionalization of the DNA biosensor?

Thiolated ssDNA probes

What gives the gold-nanorod DNA biosensor its specificity?

The ssDNA probes selectively hybridize with their complementary DNA pairs

What happens after complementary DNA hybridizes with the probes?

Nanorods self-assemble/aggregate

How does DNA-induced aggregation produce a signal?

The plasmonic coupling is changed, causing a measurable shift in the absorption spectrum

What is the DNA biosensor sequence?

CTAB coated nanorod → thiolated ssDNA probe → complementary DNA hybridization → aggregation of nanorods → plasmonic shift → detection

What is Raman scattering?

Inelastic scattering of photons from a target molecule that can provide information about chemical bonds

How does LSPR enhance Raman spectroscopy?

LSPR enhances the local electromagnetic field around the NP surface, enhancing the Raman scattering signa.

Can SPR enhance signals besides Raman scattering?

Yes, fluorescence

What is the key relationship between SPR and biosensing?

Target interaction → surface environment/coupling changes → SPR response changes → measurable optical signal