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C. Li and J.-X. Cheng
Fig. 6.10 a A single gold nanorod functionalized with biotin is introduced into an environment
with the protein of interest. Binding of the analyte molecules to the receptors induces a redshift
of the longitudinal surface plasmon resonance (exaggerated in the illustration). This shift is monitored at a single frequency using photothermal microscopy. b Photothermal time trace showing
single-molecule binding events. The normalized photothermal signal as a function of time for
biotin-functionalized gold nanorods in the presence of a streptavidin–R-phycoerythrin conjugate.
The photothermal signal was recorded on three different nanorods in the presence of different concentrations of the protein. The red lines are fits to the time traces using a step-finding algorithm.
Adapted from [123] with permission. Copyright 2012 Macmillan Publishers Limited obtained
cellular proteins that have strong absorption in the visible region are often studied
by visible excited SR-PTM [130]. The deployment of tunable pump lasers allows
the collection of absorption spectroscopy simultaneously with PT imaging, which
enabled identification, quantification, and differentiation of cytochromes c in mitochondria, live cells, and solutions [131]. The visible excited SR-PTM has also been
demonstrated in tissue histology to image nuclei (hematoxylin), cell bodies (eosin),
and melanin with H&E stained skin tissues [132]. However, the number of such
intracellular analytes is limited and cannot be applied universally. The other solution
is provided by the integration of radially segmented balanced (RSB) detection to
the conventional PTM to enhance the modulated PT signal and suppress the noise
arising from probe intensity fluctuations as well as electronic cross-talks (Fig. 6.11).
As a result, the overall SNR of the SR-PTM with RSB detection is improved by ~2.3
times [133, 134]. Such enhancement may not look dramatic but is sufficient to obtain
decent label-free images of skin tissues [133], skeletal muscle mitochondria [135],
C. Li and J.-X. Cheng
Fig. 6.10 a A single gold nanorod functionalized with biotin is introduced into an environment
with the protein of interest. Binding of the analyte molecules to the receptors induces a redshift
of the longitudinal surface plasmon resonance (exaggerated in the illustration). This shift is monitored at a single frequency using photothermal microscopy. b Photothermal time trace showing
single-molecule binding events. The normalized photothermal signal as a function of time for
biotin-functionalized gold nanorods in the presence of a streptavidin–R-phycoerythrin conjugate.
The photothermal signal was recorded on three different nanorods in the presence of different concentrations of the protein. The red lines are fits to the time traces using a step-finding algorithm.
Adapted from [123] with permission. Copyright 2012 Macmillan Publishers Limited obtained
cellular proteins that have strong absorption in the visible region are often studied
by visible excited SR-PTM [130]. The deployment of tunable pump lasers allows
the collection of absorption spectroscopy simultaneously with PT imaging, which
enabled identification, quantification, and differentiation of cytochromes c in mitochondria, live cells, and solutions [131]. The visible excited SR-PTM has also been
demonstrated in tissue histology to image nuclei (hematoxylin), cell bodies (eosin),
and melanin with H&E stained skin tissues [132]. However, the number of such
intracellular analytes is limited and cannot be applied universally. The other solution
is provided by the integration of radially segmented balanced (RSB) detection to
the conventional PTM to enhance the modulated PT signal and suppress the noise
arising from probe intensity fluctuations as well as electronic cross-talks (Fig. 6.11).
As a result, the overall SNR of the SR-PTM with RSB detection is improved by ~2.3
times [133, 134]. Such enhancement may not look dramatic but is sufficient to obtain
decent label-free images of skin tissues [133], skeletal muscle mitochondria [135],