Subnanometer dextran analysis for biosensors using a tilt stage in atomic force microscopy

• Published in: Progress in organic coatings 2022-09, Vol.170, p.106943, Article 106943
• Main Authors: Kim, Dongwan, Kim, Taeryong, Kim, Dong Hyung, Shin, ChaeHo
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; Binding; Biosensors; Dextran; Dextrans; Functional groups; Measurement methods; Microscopy; Reliability; Roughness; Scanners; Self-assembly; Step height; Tilt stage; Uncertainty analysis
• ISSN: 0300-9440; 1873-331X
• DOI: 10.1016/j.porgcoat.2022.106943

Dextran controls the characteristics of the sensor chip by providing a binding surface for bioreceptors. Therefore, the thickness and roughness of the dextran surface are important for determining the binding force and stability of the functional groups. Atomic force microscopy (AFM) can measure the shape and step height of a surface with high reliability. However, to determine a step height accurately at the sub-nm scale, the travel range of a piezo-Z scanner must be controlled and eliminate the effects of measurement errors caused by the movement of the piezo-Z scanner. In this paper, we describe the development of a tilt stage that minimizes the displacement of the piezo-Z scanner and reduces the tilt angle to 0.15° in a 10-μm square field of view. Furthermore, to improve the reliability of step-height measurements, we proposed and developed a one-step height-measurement method based on ISO 5436-1, in which the height values are determined by analyzing and classifying the surface slopes on both sides of the step. Using this measurement method and by conducting an uncertainty analysis, we confirmed that the height of a self-assembled dextran layer on a silane surface was 0.674 nm with the expanded uncertainty (k = 2) of 0.153 nm. [Display omitted] •The nonlinear effects of the piezo-Z scanner was minimized by using a developed tilt stage which achieves tilt angles as low as 0.15° in a 10-μm square FOV.•To analyze the heights of a dextran film on scales less than nanometer sizes, we developed SW based on ISO 5436-1.•To demonstrate the reliability of surface analysis, we performed an uncertainty analysis and identified the factors that have the greatest impact on the uncertainty of step-height measurements.