Table 1 |.
Representative numbers of semiconductor biointerfaces
| Scale or property |
Example | Approximate value | Refs |
|---|---|---|---|
| Length scale | |||
| Semiconductor | Minimum channel length of a FET | ~5 nm | 53,220 |
| Diameter of a Si nanowire | ~3–500 nm | 221,222 | |
| Diameter of a single-walled carbon nanotube | ~0.5–3 nm | 223 | |
| Minimum thickness of a semiconductor nanomembrane | <1 nm, 1-atom-thick or 3-atom-thick | 224 | |
| Biology | Active zone diameter of a synaptic junction | ~0.2–0.5 μm | 225 |
| Outer diameter of a microtubule and actin filament | ~25 nm (microtubule) and ~6 nm (actin filament) | 73 | |
| Diameter of a human rod cell (that is, a photoreceptor) | ~2 μm | 73 | |
| Thickness of a phospholipid bilayer | ~4 nm | 73 | |
| Timescale | |||
| Semiconductor | Si dissolution rate at physiological conditions | ~1–100 nm per day | 226 |
| Switching speed of a nanoscale FET device | Up to 2 THz | 137 | |
| Frame rate of a commercial CMOS camera | Up to 100 fps with 2,048 × 2,048 pixels, 1,600 fps with 128 × 128 pixels | 227 | |
| Lifetime of porous Si fluorescence | ~5–13 μs | 105 | |
| Biology | Duration of a seizure event | <20 min | 228 |
| Maximum firing frequency of a fast-spiking neuron | ~500–600 Hz | 229 | |
| Action potential propagation in humans or chemical signal transmission in a HeLa cell | ~10–100 ms−1 (action potential); ~1–10 (μm s−1 (signal transmission) |
73 | |
| Lifetime of tissue autofluorescence | <10 ns | 105 | |
| Electrical properties | |||
| Semiconductor | Built-in potential across a Si p-n diode junction | ~0.7 V | 8 |
| Photocurrent density of a Si-based photocathode | Up to 35 mA cm−2 | 126 | |
| Ideal Si surface potential change if pH is varied by one unit | 60 mV | 31 | |
| Noise level of CMOS-based in vivo electrophysio-logical recording tool | ~5 μV | 65 | |
| Biology | Membrane potential of undifferentiated hMSCs and neurons | ~−27 mV (hMSCs) and −70 mV (neurons) | 230 |
| Endogenous bioelectric current density in cornea wounds | ~5 μA cm−2 | 41 | |
| Electrochemical proton motive force of mitochondria | ~160 mV | 73 | |
| Extracellular field potential in the brain | ~2 mV | 231 | |
| Mechanical properties | |||
| Semiconductor | Theoretical elastic strain limit of Si | ~17–20% | 72 |
| Bending stiffness of a 10 nm-thick Si membrane | ~10−5 nN m | 81 | |
| Persistence length of a Si nanowire 5 nm in diameter | ~2 mm | 232 | |
| Sensitivity of a Si-based pressure gauge | ~2.6 Ω kPa−1 μm−1 | 16 | |
| Biology | Tensile strain of biopolymers (for example, cytoskeletal filaments) |
~10% | 233 |
| Bending stiffness of brain tissue | ~10−4-10−1 nN m | 75 | |
| Persistence length of a microtubule | ~1–5 mm | 73 | |
| Rat intracranial pressure at rest | ~1–2 kPa | 16 | |
| Energy | |||
| Semiconductor | Power output from a single Si nanowire photovoltaic device (1 sun illumination) | ~10−10–10−9 W | 56 |
| Energy released by Si hydrolysis | ~–200 kJ mol−1 | 234 | |
| Energy output from a 1 ms pulse of a 5 mW LED | 5 μJ | – | |
| Power consumption per pixel for a CMOS chip | 12 μW | 60 | |
| Biology | Power consumption of a bacterial cell | ~10−12 W | 73 |
| Gibbs free energy change during ATP hydrolysis | ~−50 kJ mol−1 or ~20 kBT | 73 | |
| Activation energy of one ChR2 ion channel | ~21 kJ mol−1 | 235 | |
| Energy required to transmit one bit of information carried by action potentials |
104 ATP or 5 × 105 kJ mol−1 for chemical synapses, ~106−107 ATP or ~5 × 107 5 × 108 kJ mol−1 for spike coding | 236 | |
The orders of magnitude of properties or processes are highlighted to suggest the feasibility of using inorganic semiconductors as biophysical tools or biomedical devices. ChR2, channelrhodopsin 2; CMOS, complementary metal-oxide-semiconductor; FET, field-effect transistor; hMSC, human mesenchymal stem cell; kB, Boltzmann constant; LED, light-emitting diode; T, temperature.