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, 3 (12), 473-490

Inorganic Semiconductor Biointerfaces


Inorganic Semiconductor Biointerfaces

Yuanwen Jiang et al. Nat Rev Mater.


Biological systems respond to and communicate through biophysical cues, such as electrical, thermal, mechanical and topographical signals. However, precise tools for introducing localized physical stimuli and/or for sensing biological responses to biophysical signals with high spatiotemporal resolution are limited. Inorganic semiconductors display many relevant electrical and optical properties, and they can be fabricated into a broad spectrum of electronic and photonic devices. Inorganic semiconductor devices enable the formation of functional interfaces with biological material, ranging from proteins to whole organs. In this Review, we discuss fundamental semiconductor physics and operation principles, with a focus on their behaviour in physiological conditions, and highlight the advantages of inorganic semiconductors for the establishment of biointerfaces. We examine semiconductor device design and synthesis and discuss typical signal transduction mechanisms at bioelectronic and biophotonic interfaces for electronic and optoelectronic sensing, optoelectronic and photothermal stimulation and photoluminescent in vivo imaging of cells and tissues. Finally, we evaluate cytotoxicity and highlight possible new material components and biological targets of inorganic semiconductor devices.


Fig. 1 |
Fig. 1 |. Milestones of inorganic semiconductor devices for biological studies.
FET, field-effect transistor; QD, quantum dot.
Fig. 2 |
Fig. 2 |. Material physics at the semiconductor-saline interface.
a | Band structures of inorganic semiconductors. The bandgap Eg is defined as the energy difference between the lowest point of the conduction band (CB) and the highest point of the valence band (VB). A semiconductor can have either an indirect or a direct bandgap. In an indirect bandgap semiconductor (for example, Si), the VB and CB edges are not aligned in the momentum space and thus the electrons in the VB cannot be directly excited to the CB without the assistance of phonons. In a direct bandgap semiconductor (for example, InP), the electron transfer between the VB and the CB occurs directly through the absorption or emission of photons. The two band structures are not to scale. b | Band edge positions of different inorganic semiconductors with respect to vacuum level and normal hydrogen electrode (NHE) potential. The redox potentials of the H2O/H2 and O2/H2O2 couples at physiological pH are drawn as references (dashed lines). Band edge positions and bandgap energies are based on data from the literature,,–. c | Band bending at semiconductor-saline interfaces. Band bending occurs if a semiconductor is immersed in a saline solution, as the charge flow between the solid and liquid phases aims to reach an equilibrium in terms of Fermi levels (EF = EF(redox)). ECB and EVB are the energies of the CB and VB edges, respectively. VSC is the semiconductor barrier height at the depletion layer. Illumination of the semiconductor causes different energy distributions of the photogenerated carriers (that is, electrons and holes (h+)) occupying the corresponding quasi-Fermi levels EF(e) and EF(h). Swept by the built-in electric field, photocarriers can be injected into the solution for surface electrochemical reactions with the corresponding redox species. DOx and DRed are the densities of states for oxidants and reductants in the saline solution, respectively.
Fig. 3 |
Fig. 3 |. Operation principles of inorganic semiconductor devices.
a | A field-effect transistor (FET) device consists of a semiconductor channel, a dielectric layer and three electrodes (source, drain and gate). The gate-source voltage (VGS) can modulate the drain-source current (IDS). The transconductance gm ∝ typically follows gmμVDS. μ is the charge carrier mobility, and VDS is the drain-source voltage. EF(G) and EF(SC) are the Fermi levels of the gate and semiconductor, respectively. ECB and EVB are the energies of the conduction band (CB) and valence band (VB) edges, respectively. b | A p-n diode junction is the key building block for optoelectronic devices. c | A photovoltaic device uses minority carriers and yields the photocurrent Iph and the photovoltage Vph. d | In a light-emitting diode (LED) device, a forward bias Vbias is applied to drive the majority carrier flow. Carrier recombination leads to light emission in direct bandgap semiconductors. hv, photon energy.
Fig. 4 |
Fig. 4 |. Semiconductor geometries and possible modes for biointerfaces.
a | 0D semiconductors can be used to mimic photosynthesis, for example, by using CdS nanoparticles that are precipitated on the cell wall of a bacterium to sensitize non-photosynthetic bacteria through photoinduced electron transfer pathways. Photoluminescent quantum dots can be coupled to motor proteins to enable the tracking of intracellular transport mechanisms. b | 1D semiconductors, for example, nanoscale kinked Si nanowire field-effect transistors, allow intracellular recordings of single cell action potentials. Nanowire-bacteria hybrids can photoelectrochemically fix carbon dioxide and produce value-added chemicals. c | 2D semiconductors, for example, biodegradable Si, provide a physically transient form of electronic devices. The photovoltaic effect of thin-film Si diode junctions can be used for the optical control of biological activities. d | 3D semiconductors, for example, semiconductor micropillar or nanopillar arrays, can detect cellular electrophysiological signals, potentially probe nucleus mechanics, deliver optical stimuli for photostimulation and release drugs. Strain-engineered 3D mesostructures of Si can serve as electronic scaffolds for neural networks. e | Typical signal transduction mechanisms of semiconductor devices involve electrical or optical inputs and outputs. Ox, oxidation; Red, reduction.
Fig. 5 |
Fig. 5 |. Biophysical mechanisms of signal transduction at semiconductor biointerfaces.
a | There are six basic operation modes of semiconductor-enabled biointerfaces. (1) A field-effect transistor can sense device-cell junctional bioelectric signals (Vj) and biomolecule concentrations (Mj) through its gate-controlled drain-source currents. (2) A photodiode can sense bioluminescence. (3) The photovoltaic effect of a semiconductor can generate a photovoltage (Vs) upon light illumination, which can locally modulate biological activities through either capacitive (Cs) or Faradaic (Zs) effects. (4) Cells can be stimulated by direct light emission using semiconductors in conjunction with other photosensitization techniques, such as optogenetics. (5) Recombination of photogenerated carriers in a semiconductor can dissipate energies through lattice-vibration-induced heating (Ts) and increase the temperature (Tm) of the cell membrane to modulate biological activities. (6) A nanoscale semiconductor can exhibit either photoelectrochemical or photothermal effect inside a cell to change the intracellular potential (Vm), the intracellular concentration of biomolecules (Mintra) and the intracellular temperature (Tintra). b | Light-induced capacitive and Faradaic effects from semiconductor surfaces. Upon light illumination, excessive charge carriers (for example, electrons) accumulate near the semiconductor surface. Subsequently, the charge imbalance at the semiconductor-electrolyte interface triggers counterions (light-green spheres) in the electrolyte to migrate to the electrode surface. Inhibition of the charge injection causes the ionic flow to charge only the Helmholtz double layer, resulting in a transient capacitive current. If charges are injected into the solution, light-produced electrons and holes cause the photoelectrochemical reduction (Red) or oxidation (Ox) of solution species (dark-green spheres), that is, cathodic or anodic reactions. In both cases, the transmembrane potentials of local cell membranes (Vm) and/or concentration of biomolecules (Mintra) can be altered. WE, CE and RE are working, counter and reference electrodes, respectively, and they are not always required for biointerface studies. The blue, light-green and dark-green spheres represent ions or molecules at the biointerface, but their size and location are not to scale. hv, photon energy.

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