Biophysics Expert

---
name: biophysics-expert
version: 1.0.0
description: Expert-level biophysics covering single molecule techniques, membrane biophysics, protein mechanics, motor proteins, ion channels, and biological imaging methods.
author: luo-kai
tags: [biophysics, single molecule, membrane, protein mechanics, ion channels, imaging]
---

# Biophysics Expert

## Before Starting
1. Which biological system? (protein, membrane, cell, tissue)
2. Structural, mechanical, or dynamic properties?
3. Experimental or theoretical approach?

## Core Expertise Areas

### Single Molecule Techniques
Optical tweezers: laser trap applies piconewton forces, measures nm displacements.
Magnetic tweezers: magnetic bead manipulation, torque and force measurements.
AFM force spectroscopy: unfold proteins and measure force-extension curves.
FRET: fluorescence resonance energy transfer, measures nanometer-scale distances.
Single molecule fluorescence: track individual molecules in living cells.

### Membrane Biophysics
Lipid bilayer: two leaflet structure, fluid mosaic model, selective permeability.
Membrane tension: controls cell shape, migration, and mechanosensing.
Patch clamp: measure single ion channel currents in picoampere range.
Lipid rafts: cholesterol-rich ordered domains, organize signaling proteins.
Vesicle mechanics: osmotic pressure, Helfrich elasticity, flickering spectroscopy.

### Protein Mechanics
Protein folding: hydrophobic collapse, hydrogen bond formation, funnel energy landscape.
Mechanical unfolding: stepwise unfolding domains detected by AFM or optical tweezers.
Motor proteins: myosin, kinesin, dynein convert chemical energy to mechanical work.
Worm-like chain: polymer model for DNA and unfolded proteins, persistence length.

### Biological Imaging
Confocal microscopy: optical sectioning, fluorescence, subcellular resolution.
TIRF: total internal reflection fluorescence, single molecule sensitivity at surface.
STORM and PALM: super-resolution beyond diffraction limit, 20nm resolution.
Cryo-EM: near-atomic resolution protein structures, complement to X-ray crystallography.

## Best Practices
- Always include appropriate controls for fluorescence experiments
- Correct for photobleaching in long single molecule recordings
- Validate single molecule observations with ensemble measurements
- Consider thermal fluctuations in all nanoscale measurements

## Common Pitfalls
| Pitfall | Fix |
|---|---|
| Ignoring thermal noise at nanoscale | kBT = 4 pN nm, comparable to biological forces |
| Fluorescent label affecting protein function | Test labeled vs unlabeled activity |
| Surface effects in single molecule assays | Use appropriate blocking and surface chemistry |
| Confusing correlation with mechanism | Mechanistic interpretation needs additional experiments |

## Related Skills
- cell-biology-expert
- molecular-biology-expert
- physics/quantum-mechanics-expert