Label-free multiplex sensing from buffer and immunoglobulin G sensing from whole blood with photonic crystal slabs using angle-tuning of an optical interference filter

Direct detection of biomarkers from unpurified whole blood has been a challenge for label-free detection platforms, such as photonic crystal slabs (PCS). A wide range of measurement concepts for PCS exist, but exhibit technical limitations, which render them unsuitable for label - free biosensing with unfiltered whole blood. In this work, we single out the requirements for a label-free point-of-care setup based on PCS and present a wavelength selecting concept by angle tuning of an optical interference filter, which fulfills these requirements. We investigate the limit of detection (LOD) for bulk refractive index changes and obtain a value of 3.4 E-4 refractive index units (RIU). We demonstrate label-free multiplex detection for different types of immobilization entities, including aptamers, antigens, and simple proteins. For this multiplex setup we detect thrombin at a concentration of 6.3 mu g/ml, antibodies of glutathione S-transferase (GST) diluted by a factor of 250, and streptavidin at a concentration of 33 mu g/ml. In a first proof of principle experiment, we demonstrate the ability to detect immunoglobulins G (IgG) from unfiltered whole blood. These experiments are conducted directly in the hospital without temperature control of the photonic crystal transducer surface or the blood sample. We set the detected concentration levels into a medical frame of reference and point out possible applications.(c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

Direct detection of biomarkers from unpurified whole blood using label-free detection platforms has been a challenge. In this study, a wavelength selecting concept based on photonic crystal slabs (PCS) is proposed to address the technical limitations and enable label-free point-of-care biosensing with unfiltered whole blood. The researchers achieved a limit of detection of 3.4 E-4 refractive index units (RIU) for bulk refractive index changes and demonstrated multiplex detection of different immobilization entities. The ability to detect immunoglobulins G (IgG) from unfiltered whole blood was also demonstrated.