Label-free OIRD microarray chips with a nanostructured sensing interface: enhanced sensitivity and mechanism

Label-free OIRD detection of protein microarrays on high dielectric constant substrate with enhanced intrinsic sensitivity

Oblique-incidence reflectivity difference (OIRD) is a dielectric constant-sensitive technique and exhibits intriguing applications in label-free and high-throughput detection of protein microarrays. With the outstanding advantage of being compatible with arbitrary substrates, however, the effect of the substrate, particularly its dielectric constant on the OIRD sensitivity has not been fully disclosed. In this paper, for the first time we investigated the dependence of OIRD sensitivity on the dielectric constant of the substrate under top-incident OIRD configuration by combining theoretical modeling and experimental evaluation. Optical modeling suggested that the higher dielectric constant substrate exhibits a higher intrinsic sensitivity. Experimentally, three substrates including glass, fluorine-doped tin oxide (FTO) and silicon (Si) with different dielectric constants were selected as microarray substrates and their detection performances were evaluated. In good agreement with the modeling, high dielectric constant Si-based microarray exhibited the highest sensitivity among three chips, reaching a detection limit of as low as 5 ng mL-1 with streptavidin as the model target. Quantification of captured targets on three chips with on-chip enzyme-linked immunosorbent assay (ELISA) further confirmed that the enhanced performance originates from the high dielectric constant enhanced intrinsic OIRD sensitivity. This work thus provides a new way to OIRD-based label-free microarrays with improved sensitivity.

Gold nanoparticle-decorated fluorine-doped tin oxide substrate for sensitive label-free OIRD microarray chips

Oblique incidence reflectance difference (OIRD) is an emerging technique enabling real-time and label-free detection of bio-affinity binding events on microarrays. The interfacial architecture of the microarray chip is critical to the performance of OIRD detection. In this work, a sensitive label-free OIRD microarray chip was developed by using gold nanoparticle-decorated fluorine-doped tin oxide (AuNPs-FTO) slides as a chip substrate. This AuNPs-FTO chip demonstrates a higher signal-to-noise ratio and improved sensitivity compared to that built on FTO glass, showing a detection limit of as low as 10 ng mL-1 for the model target, HRP-conjugated streptavidin. On-chip ELISA experiments and optical calculations suggest that the enhanced performance is not only due to the higher probe density enabling a high capture efficiency toward the target, but most importantly, the AuNP layer arouses optical interference to improve the intrinsic sensitivity of OIRD. This work provides an effective strategy for constructing OIRD-based microarray chips with enhanced sensitivity, and may help extend their practical applications in various fields.

Label-Free and Real-Time Optical Detection of Affinity Binding of the Antibody on Adherent Live Cells

Oblique-incidence reflectivity difference (OIRD) is a novel real-time, label-free, and nondestructive optical detection method and exhibits encouraging application in the detection of antibody/DNA microarrays. In this study, for the first time, an OIRD label-free immunoassay was achieved by using adherent live cells as the probe. The cells were cultured on glass cells, and the affinity binding of antibodies targeted on the HLA class I antigen of the cell surface was detected with an OIRD. The results show that an OIRD is able to detect the binding process of anti-human HLA-A, B, and C antibodies on MDA-MB-231 cells and HUVEC cells. Control experiments and complementary fluorescence analysis confirmed the high detection specificity and good quantitative virtue of the OIRD label-free immunoassay. Label-free OIRD imaging analysis of cell microarrays was further demonstrated successfully, and the underlying optical mechanism was revealed by combining the theoretical modeling. This work explores the use of live cells as probes for an OIRD immunoassay, thus expanding the potential applications of the OIRD in the field of pathological analysis, disease diagnosis, and drug screening, among others.

Optical Approach for Mapping the Intercalation Capacity of Porous Electrodes

The intercalation capacity of a porous electrode in real batteries is not uniform spatially due to the inevitable structural and compositional inhomogeneity and site-dependent ion and electron transport features. Reliable methods to quantify the capacity distribution are highly desirable but absent so far in battery research. In this paper, a novel optical technique, oblique incident reflection difference (OIRD), was employed to monitor in situ the electrochemical ion (de)intercalation behavior of Prussian blue analogue (PBA) porous films. The OIRD signal responded synchronously to the ion (de)intercalation, and the change in the OIRD signal (ΔI) was positively correlated with the local electrochemical capacity, thereby enabling mapping of the spatially resolved ion storage capacity of the films. Optical analysis further showed that the OIRD response originated from the ion (de)intercalation-induced dielectric constant change of PBA films. This work therefore offers an intriguing in situ and spatially resolved tool for the study of rechargeable batteries.

Non-fouling polymer brush grafted fluorine-doped tin oxide enabled optical and chemical enhancement for sensitive label-free antibody microarrays

Oblique-incidence reflectivity difference (OIRD) is a compelling technique for real-time, label-free and non-destructive detection of antibody microarray chips, but its sensitivity needs essential improvement for clinical diagnosis. In this study, we report an innovative high-performance OIRD microarray by using poly[oligo(ethylene glycol) methacrylate-co-glycidyl methacrylate] (POEGMA-co-GMA) brush grafted fluorine-doped tin oxide (FTO) as the chip substrate. The polymer brush enhances the interfacial binding reaction efficiency of targets from the complicated sample matrix due to its high antibody loading and excellent anti-fouling merits; the FTO-polymer brush layered structure, on the other hand, excites the interference enhancement effect of OIRD to achieve enhanced intrinsic optical sensitivity. Synergistically, the sensitivity of this chip is significantly improved compared to rival chips, achieving a limit of detection (LOD) as low as 25 ng mL^-1 for the model target C-reactive protein (CRP) in 10% human serum. This work explores the tremendous influence of the chip interfacial structure on the OIRD sensitivity and proposes a rational interfacial engineering strategy to boost the performance of the label-free OIRD based microarray and other bio-devices.