Diverse Dyes-Embedded Staphylococcus aureus as Potential Biocarriers for Enhancing Sensitivity in Biosensing

Area of Science:

• Bioconjugation Chemistry
• Nanomaterials Science
• Analytical Chemistry
• Point-of-Care Diagnostics

Background:

• Nanomaterials-based immunochromatographic assays (ICAs) are vital for point-of-care testing (POCT).
• Developing sensitive POCT requires novel ICA carriers with enhanced signaling and stability.
• Traditional nanomaterials face limitations in signal amplification and antibody immobilization.

Purpose of the Study:

• To develop a novel, highly sensitive signal biotag for ICA carriers.
• To utilize colored *Staphylococcus aureus* (SA) as a biocompatible carrier for monoclonal antibody (mAb) immobilization.
• To demonstrate the application of SA-based ICAs for sensitive zearalenone (ZEN) detection.

Main Methods:

• A mild self-assembly strategy was employed to create colored *Staphylococcus aureus* (SA) dyes (SADs).
• Monoclonal antibodies (mAbs) were immobilized onto SADs via their Fc portion, preserving bioactivity.
• Congo red- and/or fluorescein isothiocyanate-embedded SA (SACR, SAFITC, SACR-SAFITC) were used as ICA carriers for ZEN detection.

Main Results:

• SA-dyes (SADs) provided high luminance and abundant binding sites for mAbs, retaining antibody bioactivity (affinity constant ~10^9 M^-1).
• The developed ICAs achieved a limit of detection of 0.013 ng/mL for ZEN, an 85-fold improvement over traditional gold nanoparticle-based ICAs.
• The biosensors demonstrated excellent linearity (R^2 > 0.98), reproducibility (RSD < 8%), selectivity, stability, and successful application in real samples.

Conclusions:

• Colored *Staphylococcus aureus* (SA) serves as a potent, biocompatible signal biotag for sensitive immunochromatographic assays (ICAs).
• The proposed SA-dye based ICAs (SAD-ICAs) offer a universal platform for detecting multiple analytes with high sensitivity and clinical applicability.
• This approach overcomes limitations of traditional nanomaterials and advances the development of next-generation point-of-care testing (POCT) devices.