(a) Coupling media PA transmission results. Transmission of HWG and WG at 2% and 3% w/w gellan concentrations are displayed, along with D 2 O (100% concentration, pure), D 2 O (99% concentration, 1% H 2 O) and H 2 O (100% concentration, pure) calculated transmission via absorption coefficients 20 through an identical pathlength Δz ¼ 10 mm. (b) Laser energy measurements of the reflection-mode setup through samples of HWG and WG (thickness ∼5.0 mm) with the horizontal line denoting the cut-off energy threshold of 1 mJ.

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... mode data is tabulated and graphed in Fig. 4. The relative PA signals across the band are normalized to black tape for comparing each coupling medium. It is observed that the PA transmission spectrum of HWG (2% and 3% w/w) is similar to the Beer-Lambert signal for 99% heavy water with the same optical pathlength. Energy measurements of the LAZR-X fiber bundle through 2% w/w HWG ...

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... PA signals across the band are normalized to black tape for comparing each coupling medium. It is observed that the PA transmission spectrum of HWG (2% and 3% w/w) is similar to the Beer-Lambert signal for 99% heavy water with the same optical pathlength. Energy measurements of the LAZR-X fiber bundle through 2% w/w HWG and WG are displayed in Fig. 4. We set a criterion that laser illumination reaching the samples with <1 mJ energy was insufficient for producing PA images with adequate SNR. The WG coupling agent, for example, strongly absorbed light above 1350 nm. Light delivery through HWG, on the other hand, maintained sufficient light delivery to the sample (>1 mJ) across the ...

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... nm. Light delivery through HWG, on the other hand, maintained sufficient light delivery to the sample (>1 mJ) across the entire SWIR region up to 1850 nm. PA signals were too weak or undetectable outside these cutoff wavelengths. An assessment of the stability of HWG transmission between two time points was also conducted. The HWG sample used in Fig. 4 was tested 60 days after storage in an airtight zip bag stored in a refrigerator at 4°C. Energy measurements after 60 days yielded no significant transmission change (average difference: 1.06 AE 0.49 mJ), demonstrating the stability of HWG with proper storage. ...

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... lipids. PA surface spectra are plotted for the samples in Fig. 7, demonstrating signals above noise for HWG across this full range, including distinct peaks of lipid/water. At 1220 nm, a 7.5 dB signal increase is observed at the surface of the phantom using HWG compared to WG. This agrees closely with what is expected via the absorption plots in Fig. 4 through a similar optical pathlength at 1220 nm. At a depth of 4.5 mm into the sample, a 4.6 dB signal increase is observed, indicating at depth an SNR increase of nearly 2× is apparent with HWG coupling compared to WG coupling at shorter SWIR wavelengths. For this sample, the noise floor is reached through HWG at a depth of ∼5 mm. At ...

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... enables PAI of tissue samples across a broad spectral range in the SWIR (1200 to 1850 nm), whereas WG is limited to wavelengths <1350 nm with poor SNR (Fig. 4). It was anticipated that the predicted transmission spectrum of HWG would be similar to that of heavy water in liquid form at the equivalent concentration (99% pure). The results align with this prediction, as illustrated in Fig. 4. Slight shifts in the transmission peaks in the WG sample compared to baseline are likely due to the ...

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... a broad spectral range in the SWIR (1200 to 1850 nm), whereas WG is limited to wavelengths <1350 nm with poor SNR (Fig. 4). It was anticipated that the predicted transmission spectrum of HWG would be similar to that of heavy water in liquid form at the equivalent concentration (99% pure). The results align with this prediction, as illustrated in Fig. 4. Slight shifts in the transmission peaks in the WG sample compared to baseline are likely due to the bonding mechanism of the low-acyl gellan gum, which has been reported previously. 41,42 This effect is also observed with HWG, indicating the bonding effects of gellan and heavy water are similar to that of WG. Akin to water-based ...