Table 1 Micro/nano devices for intracellular measurements
Measurement | Technique | Description | References |
|---|---|---|---|
Electrical properties | 3D kinked silicon nanowire | NanoFET built on kinked nanowire; phospholipid bilayer coated; sensitivity: 4∼8 μS/V for conductance measurement; capable of pH measurement with a 58 mV/pH sensitivity | |
Branched nanoFET | Hollow SiO2 structure; 5 nm probe size with controlled taper tip | ||
Multielectrode arrays | Parallel sensing; higher throughput; unknown disturbance to cell activities; unable to control individual insertion depth | ||
Carbon nanotube | High tensile strength and elastic modulus; high electric current density; 100∼200 nm tip size | ||
Mechanical properties | Modified AFM tip | Fabricated via FIB or direct growth/assembly of nanowires on AFM tips; capable of measuring nuclear mechanics and mapping intracellular stiffness; 30∼180 nm tip diameter; 0.5∼6 μm tip height | |
Vinculin-fused fluorescent protein (FP) | Force sensitive focal adhesion proteins tagged with GFP used to visualize the formation of local complex in response to local forces | ||
Cdc42/Src-specific FP | Local mechanical stimulation induces changes in the FRET level of Cdc42/Src-specific fluorescent signal | ||
Lamin-A/Fib GFP | GFPs conjugated to nuclear Lamin-A or Fib reveal the shape and motion changes of nucleus in response to mechanical stimulation | ||
Temperature | CdSe quantum dots | Temperature changes convert to spectrum shift; first experimental demonstration of heterogeneous intracellular temperature | |
Polymetric nanoparticles | Consist of a thermosensitive unit, a hydrophilic unit, and a fluorescent unit; 0.18∼0.58 °C resolution; 0.96 °C average temperature variance in COS7 cells | ||
Nanodiamond | Ultrahigh 1.8 mK resolution; thermally induced lattice strains cause the changes in transition frequency | ||
GFP | Intracellular temperature variations cause GFP characteristic changes in blinking relaxation time or polarization anisotropy | ||
Chemical sensing (e.g., pH, Ca2+, Cu2+, Cl−) | Dual-emission nanoparticle | Incorporation of a sensing dye and analyte insensitive reference dye enables ratio metric measurement | |
Core-shell nanoparticle | A reference-dye-rich core coated with a thin layer of sensing-dye-rich silica shell; measured endosome pH varying from 5.0 to 6.5 | ||
GFP | Fluorescence and absorbance properties of mutant GFP reflect intracellular pH level | ||
Pressure | MEMS sensor | Intracellular pressure deflects device membrane and alters the intensity of reflected light; introduced into cell via lipofection; device size: 4 × 6 × 0.4 μm | |
Optical measurement | SiO2 nanowire | Works as either a light source for imaging or a spectrometer to collect optical signal; can be coupled with untethered nanoparticles to measure intracellular pH or temperature; 100∼250 nm tip size |
