Mid‐Infrared Photoacoustic Stimulation of Neurons through Vibrational Excitation in Polydimethylsiloxane
Zhiyi Du, Mingsheng Li, Guo Chen, Maijie Xiang, Danchen Jia, Ji‐Xin Cheng, Chen Yang
Advanced Science 2024, 11 · 10.1002/advs.202405677
Abstract
Photoacoustic (PA) emitters are emerging ultrasound sources offering high spatial resolution and ease of miniaturization. Thus far, PA emitters rely on electronic transitions of absorbers embedded in an expansion matrix such as polydimethylsiloxane (PDMS). Here, it is shown that mid-infrared vibrational excitation of C─H bonds in a transparent PDMS film can lead to efficient mid-infrared photoacoustic conversion (MIPA). MIPA shows 37.5 times more efficient than the commonly used PA emitters based on carbon nanotubes embedded in PDMS. Successful neural stimulation through MIPA both in a wide field with a size up to a 100 µm radius and in single-cell precision is achieved. Owing to the low heat conductivity of PDMS, less than a 0.5 °C temperature increase is found on the surface of a PDMS film during successful neural stimulation, suggesting a non-thermal mechanism. MIPA emitters allow repetitive wide-field neural stimulation, opening up opportunities for high-throughput screening of mechano-sensitive ion channels and regulators.
Abstract via europepmc.
Exposures
Exposure 1: Mid-infrared photoacoustic (MIPA) stimulation of cultured cortical neurons on PDMS film (wide-field and high-precision/focused modes)
Target: cultured neurons — “DIV12 primary rat cortical neurons cultured on the top surface of a PDMS film”
Device: custom-built
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 10,000 | ✓✓✓⚑ |
| Pulse duration (ms) | not reported | |
| Pulse repetition frequency (Hz) | 150,000 | ✓✓✓ |
| Duty cycle (%) | not reported | |
| Sonication duration (s) | 0.005, 0.015swept | ✓✓✓ |
| Free-field pressure (kPa) | 12.35, 696swept | ✓✓✓ |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not applicable | |
| In-situ pressure (kPa) | not applicable | |
| In-situ Isppa (W/cm²) | not applicable | |
| In-situ Ispta (W/cm²) | not applicable |
Wide-field mode: a 5-ms laser pulse train with a repetition rate of 150 kHz and 0.4 uJ pulse energy was weakly focused to a 200 um diameter spot (71 um PDMS film), producing 12.35 kPa PA pressure at the top surface. High-precision (focused) mode: 0.1 uJ pulse energy and a 15 ms burst duration, tightly focused to a ~10 um spot (25 um PDMS film), producing 696 kPa PA pressure at the top surface. The duration of MIR pulse trains could be chopped from 5 to 30 ms for single-shot and repeated stimulations, and other durations (10, 20, 30, 100 ms) were used for viability/thermal characterization.
Flags from extraction
exposures[0].fundamental_frequency_khz— This is a broadband photoacoustic pulse's measured central frequency (10 MHz), not a conventional continuous-wave carrier frequency; recorded as stated but the concept differs from typical piezoelectric TUS.exposures[0].in_situ— Pressure values are calculated at the PDMS surface (where neurons are cultured) from a measured 1/r pressure-distance fit, not a brain/skull in-situ value in the usual TUS sense; classified as in_situ (at-target) by analogy, domain assignment is a judgement call.exposures— Paper reports two distinct MIPA stimulation configurations (wide-field vs focused single-cell) at the same cultured-neuron target and central PA frequency; combined into one exposure with parameter lists per the one-exposure-per-target-and-frequency rule.n_subjects— Paper reports different neuron counts (n) for different sub-experiments (e.g., n=12, n=92) but no single total number of neurons/cultures exposed across the whole study.timing.pulse_duration_ms— Individual acoustic pulse duration within each MIR laser burst is not stated in ms (only the 10 ns laser pulse width and the overall ms-scale burst/train duration are given).