Overview: HEPES Buffered Saline (HBS)

HEPES buffered saline (HBS) is a biological buffer solution used to maintain stable pH and physiological ionic conditions across a variety of life science and analytical workflows. Built around the zwitterionic buffering agent HEPES—part of the Good’s buffer family known for low biological interference—HBS delivers consistent pH control near neutral conditions (≈7.2–7.6), even outside traditional CO₂-controlled environments.

Beyond standard HBS, specialized formulations like HBS-EP, HBS-EP+, HBS-P+, and related saline systems provide enhanced performance for Surface Plasmon Resonance (SPR) and other high-sensitivity interaction studies. 

HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) is a zwitterionic buffer that resists pH changes in the physiological range (~6.8–8.2). By itself, HEPES stabilizes hydrogen ion activity, minimizing rapid pH shifts. When combined with saline (e.g., NaCl), the result is HEPES buffered saline (HBS), a solution that also mimics physiological ionic strength for biological systems.

Why “buffered saline”?
Adding saline to a buffer provides isotonic conditions that more closely resemble the fluid environment inside living organisms and cells, which can be important for maintaining protein conformation, cell viability, and accurate measurement in analytical systems.

Typical composition of HEPES buffered saline includes:

• HEPES, primary buffering agent that controls hydrogen ion concentration
• Sodium chloride (NaCl), provides osmotic balance
• pH adjusted (commonly to ~7.4) using NaOH or HCl

The pH is tailored to physiological conditions (often ~7.4) while preserving HEPES’s buffering capacity in the range where many cells and proteins are most stable.

Core Benefits of HBS Composition

• Stable pH near physiological levels in open systems
• Low UV absorbance, making HBS suitable for optical detection methods
• Minimal biological interference, supporting protein and cell assays

Standard HEPES Buffered Saline (HBS)

Best for:

• Cell culture buffering outside CO₂ control
• Protein stabilization and enzymatic assays
• Immunological assays and flow cytometry
• Transfection mixtures and protein isolation workflows

These formulations add chelators and surfactants to the base HBS to enhance performance in Surface Plasmon Resonance (SPR):

Composition Highlights:

• HEPES: primary buffer
• NaCl: ionic strength
• EDTA: chelates divalent cations, reducing nonspecific interactions
• Tween-20 (polysorbate): non-ionic surfactant that minimizes surface and protein aggregation

HEPES buffered saline is a key reagent for multiple steps in SPR analysis. SPR, an acronym for surface plasmon resonance, is an analysis technique for assessing binding characteristics and related biochemical dynamics between molecules [1,2]. HEPES buffered saline is used to prime SPR in-unit pumps. HEPES-buffered saline formulations are tailored to specific experimental needs, serving as both a running buffer and a binding buffer in SPR workflow. These formulations contain identical concentrations of HEPES and sodium chloride but incorporate polysorbate P20 (also known as Tween-20) as a detergent and/or EDTA as a chelating agent. Tween-20 is often used at 0.005% (v/v) concentrations in HEPES EP buffers while at 0.05% concentrations in EP+ buffers. Other HBS buffer used is: HBS-N (HEPES and NaCl solution).

Best Practices

• Adjust pH at experimental temperature to ensure target pH is achieved in working conditions.
• Protect HEPES solutions from prolonged light exposure, which can accelerate degradation.
• Use sterile filtration (e.g., 0.22 µm) for biological or cell-based applications.
• Confirm compatibility with assay detection methods (e.g., UV absorbance, fluorescence).