Preparation of Economical and Universal Compensation Beads Compatible for Multi-species Antibodies

Summary

This protocol describes a cost-effective method for preparing multi-species-compatible compensation beads for fluorescence compensation in flow cytometry using recombinant Protein A/G/L–coupled polystyrene microspheres.

Abstract

This protocol describes a cost-effective and reproducible method for preparing multi-species-compatible compensation beads for fluorescence compensation in multicolor flow cytometry. Here, recombinant the immunoglobulin binding protein A/G/L (Protein A/G/L) containing multiple immunoglobulin-binding domains was expressed in Escherichia coli (E. coli), purified using nickel affinity chromatography, and covalently coupled to carboxylated polystyrene microspheres through EDC/NHS chemistry. The resulting beads bind antibodies from diverse species and subclasses, generating strong and distinct fluorescence signals suitable for compensation setup. These results provide practical guidance for selecting bead diameter and protein loading to achieve fluorescence intensities appropriate for different compensation requirements. Successful execution of the protocol is indicated by efficient protein purification and a clear, high-intensity fluorescence peak of conjugated beads compared with control beads during flow cytometry analysis. This simple and scalable approach enables routine preparation of stable, versatile compensation beads in standard laboratories, reducing cost while improving flexibility for flow cytometry applications.

Introduction

Flow cytometry has become an indispensable tool in immunology, cell biology and clinical research for multi-parametric analysis of cell populations^1,2,3. A critical challenge in traditional multi-colour flow cytometry is fluorescence spillover, wherein the emission spectrum of a fluorochrome overlaps into multiple detector channels, leading to signal contamination and erroneous interpretation^4,5. Therefore, proper compensation is essential for accurate data interpretation.

Traditionally, co....

Protocol

NOTE: Prepare all buffers and reagents freshly as listed in Table 1. Prepare EDC and NHS solutions immediately before use; do not store them. For all other buffers (Lysis, Binding, Washing, Elution, MES, PBS, Tris), prepare stock solutions in advance and store them at 4 °C. Equilibrate stored buffers to the appropriate reaction temperature (room temperature or 4 °C) before use. Ensure FACS buffer and Storage buffer are prepared freshly or stored at 4 °C.

1. Expression and purification of recombinant protein A/G/L

1. Expression of recombinant protein A/G/L
   1. Transform the pE....

Results

The recombinant fusion Protein A/G/L consists of 816 amino acids with a calculated molecular weight of 90.5 kDa (Supplementary File 1). This fusion protein retains five IgG-binding B domains from Protein A, two IgG-binding domains from Protein G, and five κ light chain-binding B domains from Protein L, while the albumin-binding domain was removed (Figure 1A, Supplement Table 1). A cysteine residue was added to the C-terminus to facilitate covalent attachment.......

Discussion

This protocol describes a practical and efficient workflow for the preparation of fluorescent compensation beads based on recombinant Protein A/G/L. The procedure includes bacterial expression, Ni-NTA affinity purification, and covalent coupling of the purified protein to carboxyl-modified polystyrene microspheres using EDC/NHS chemistry. The resulting beads can bind antibodies from multiple species and subclasses, providing a versatile and cost-effective tool for fluorescence compensation in flow cytometry.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
AF647 Rat Ig2a	BioLegend	141711
APC Mouse IgG1	BioLegend	353311
BL21(DE3) Competent Cells	Sangon	B528414
BSA	Solarbio	A8010
EDC	Thermo Fisher	22980	CAS: 1892-57-5
FITC Armenian Hamster IgG	BioLegend	400905
Imidazole	Sigma-Aldrich	I202	CAS: 288-32-4
IPTG	GoldBio	I2481C	CAS: 367-93-1
Kanamycin	Sangon	A600286	CAS: 8063-07-8
KCl	Aladdin	P112134	CAS: 7447-40-7
KH2PO4	Aladdin	P434010	CAS: 7778-77-0
MES	Sigma-Aldrich	M3671	CAS: 145224-94-8
Na2HPO4	Aladdin	S274390	CAS: 7558-79-4
NaCl	Aladdin	C111549	CAS: 7647-14-5
NHS	Thermo Fisher	24500	CAS: 6066-82-6
Ni NTA Beads 6FF	Smart-Lifesciences	SA005005
PE mouse IgG2a	BioLegend	362603
ProClean 300	Beyotime	ST853
Tris	Sigma-Aldrich	252859	CAS: 77-86-1
Tryptone	Oxoid	LP0042
Ultra Centrifugal Filter, 50 kDa MWCO	Millipore	UFC9050
Uniform Carboxyl Polystyrene Microspheres	Tomicro Biotech	10ml, 25mg/ml	Shanghai, China
Yeast Extract	Oxoid	LP0021