This document summarizes two photoacoustic detection projects using photonic crystal substrates and gold nanoparticles. The first project showed enhanced photoacoustic detection of dyes and gold nanoparticles on a 1D photonic crystal substrate due to guided-mode resonance. The second project aims to use photoacoustic detection and gold nanoparticles conjugated with biotin to quantify the surface concentration of streptavidin molecules with potential for single molecule detection. Challenges and improvements discussed include simplifying the surface chemistry preparation.
2. ENHANCED PHOTOACOUSTIC DETECTION
USING A PHOTONIC CRYSTAL SUBSTRATE
• Relevant Terminologies:
Photoacoustic (PA) effect: a kind of
photothermal effect that happens when absorbing
substance is periodically exposed to light and
periodically generates heat that induce pressure waves
in surrounding media.
Photonic crystal (PC): a material that has a
periodic structure in terms of refractive index. Such
material supports guided-mode resonance (GMR) that
induces enhanced local electric field (basically of
interference nature).
3. ENHANCED PHOTOACOUSTIC DETECTION
USING A PHOTONIC CRYSTAL SUBSTRATE
• Project outline:
Quantitative detection of absorbing dye and
gold nanoparticles (AuNPs) spread on a 1-D PC
substrate using PA method and comparison of on-
resonance and off-resonance conditions showing
the enhancement caused by GMR.
4. ENHANCED PHOTOACOUSTIC DETECTION
USING A PHOTONIC CRYSTAL SUBSTRATE
• Advantages over fluorescence methods and
prospect of the project:
1. PA detection is based on absorption.
2. Low cost instrumentations
3. Label-free when detecting AuNPs
4. No significant bleaching
5. Single particle level sensitivity when combined
with PC leading to promising prospect of single
molecule detection
5. ENHANCED PHOTOACOUSTIC DETECTION
USING A PHOTONIC CRYSTAL SUBSTRATE
• Schematics of instrumentations:
1. PC structure: TiO2 refractive index: ~2.60 at 600
nm, UVCP and acrylic: ~1.50
7. ENHANCED PHOTOACOUSTIC DETECTION
USING A PHOTONIC CRYSTAL SUBSTRATE
• Experiment results
Incident angle dependence of GMR PC enhancement by GMR on the detection of Epolight 5262
9. PA DETECTION OF STREPTAVIDIN USING
AUNPS
• Relevant Terminologies:
• Streptavidin:
A 52.8 kDa protein purified from
the bacterium Streptomyces avidinii. Streptavidin homo-
tetramers have an extraordinarily high affinity for biotin (also
known as vitamin B7 or vitamin H). With a dissociation
constant (Kd) on the order of ≈10−14 mol/L, the binding of biotin
to streptavidin is one of the strongest non-covalent interactions
known in nature. Streptavidin is used extensively in molecular
biology and bionanotechnology due to the streptavidin-biotin
complex's resistance to organic solvents, denaturants
(e.g. guanidinium chloride), detergents (e.g. SDS, Triton),
proteolytic enzymes, and extremes of temperature and pH.
10. PA DETECTION OF STREPTAVIDIN
USING AUNPS
• Project outline
• Quantitative detection of streptavidin (SA) using
AuNPs conjugated with biotin with PA method.
The specific binding of SA and biotin makes it
possible to determine the surface concentration
of SA molecules by determining the
concentration of AuNPs bound to them using PA
method.
11. PA DETECTION OF STREPTAVIDIN USING
AUNPS ON ACRYLIC SUBSTRATE
• Advantages of PA detection:
• Low cost instrumentations
• No bleaching
• High sensitivity: single molecule level detection
12. PA DETECTION OF STREPTAVIDIN USING
AUNPS ON ACRYLIC SUBSTRATE
• Schematics of the instrumentations
13. PA DETECTION OF STREPTAVIDIN
USING AUNPS ON ACRYLIC SUBSTRATE
• Preliminary results
• AuNP diluted 10x on acrylic reaction time 2 mins:
Without SA, With 0.1 g/L SA, 25 μL
PA: barely recognizable 5~10 mV spread on ~100 mm2
PA: ~100 mV
14. PA DETECTION OF STREPTAVIDIN USING
AUNPS ON ACRYLIC SUBSTRATE
• Preliminary results
15. PA DETECTION OF STREPTAVIDIN
USING AUNPS ON ACRYLIC SUBSTRATE
• Potential drawback of the new project: lengthy
surface chemistry preparation (low error-tolerance):
PVA-GA-SA-BSA, with each incubation steps
taking several hours and washings between steps.
• Methods to improve: use of glass slides or
microparticles as substrates to simplify surface
chemistry or circumvent it altogether. The latter
changes the basic outline of the project to focusing
on quantification of AuNPs on microparticles.
