Step 1: Define Your Research Question
Every protocol starts with a clear, testable question. Vague objectives lead to unfocused experiments and ambiguous results. Frame your question specifically: not merely what does this peptide do, but rather does this peptide at these concentrations affect this specific measurable outcome in this specific experimental system.
Step 2: Literature Review
Before designing your protocol, review published research on your peptide of interest. Key information to extract: concentration ranges used by other researchers, incubation times, cell types or model organisms studied, endpoints measured, and any reported stability or solubility issues. This literature foundation prevents reinventing the wheel and helps you choose meaningful experimental parameters.
Step 3: Compound Selection and Sourcing
Select a peptide source that provides batch-specific COA with HPLC purity data. Record the supplier, lot number, stated purity, and molecular weight. Verify the molecular weight matches published values for your target peptide. If comparing results across experiments, using the same lot number eliminates compound quality as a variable.
Step 4: Concentration Planning
Design a concentration range based on published literature. A typical dose-response experiment uses 5-8 concentrations spanning 2-3 orders of magnitude around the expected active range. Include a vehicle control (solvent without peptide) and, if possible, a positive control compound with known activity in your assay.
Calculate reconstitution volumes to achieve stock concentrations that allow convenient dilution to your working concentrations. Prepare a dilution scheme in advance and verify the math before reconstituting.
Step 5: Controls
Vehicle control: The reconstitution solvent alone, at the same volume used in treated samples. Essential for distinguishing peptide effects from solvent effects.
Positive control: A compound known to produce the effect you are measuring. Validates that your assay is working correctly in each experiment.
Negative control: A peptide known NOT to affect your endpoint, at the same concentration range. Distinguishes specific from non-specific peptide effects.
Step 6: Replication and Statistics
Plan for sufficient biological and technical replicates before starting. Biological replicates (independent experiments) establish reproducibility. Technical replicates (multiple measurements within one experiment) establish measurement precision. Most journals require a minimum of three biological replicates for publication.
Step 7: Documentation
Record everything in real time, not from memory. Include peptide lot number, reconstitution date, solvent used, stock concentration, working concentrations, preparation method, storage conditions, and any deviations from the planned protocol. This documentation is essential for troubleshooting and for enabling other researchers to reproduce your work.
