Large colloidal probes for atomic force microscopy: fabrication and calibration issues

TL;DR

This paper discusses the fabrication, unique dynamics, and calibration of large colloidal probes in atomic force microscopy, enhancing force measurement accuracy for micro and nanoscale investigations.

Contribution

It introduces a new protocol for calibrating the spring constant of large colloidal probes, addressing their poorly understood dynamics.

Findings

Large colloidal probes exhibit distinct dynamical behavior.

A novel calibration protocol improves spring constant accuracy.

Enhanced force measurement reliability in AFM applications.

Abstract

Atomic force microscopy (AFM) is a powerful tool to investigate interaction forces at the micro and nanoscale. Cantilever stiffness, dimensions and geometry of the tip can be chosen according to the requirements of the specific application, in terms of spatial resolution and force sensitivity. Colloidal probes (CPs), obtained by attaching a spherical particle to a tipless (TL) cantilever, offer several advantages for accurate force measurements: tunable and well-characterisable radius; higher averaging capabilities (at the expense of spatial resolution) and sensitivity to weak interactions; a well-defined interaction geometry (sphere on flat), which allows accurate and reliable data fitting by means of analytical models. The dynamics of standard AFM probes has been widely investigated, and protocols have been developed for the calibration of the cantilever spring constant. Nevertheless the dynamics of CPs, and in particular of large CPs, with radius well above 10 um and mass comparable, or larger, than the cantilever mass, is at present still poorly characterised. Here we describe the fabrication and calibration of (large) CPs. We describe and discuss the peculiar dynamical behaviour of CPs, and present an alternative protocol for the accurate calibration of the spring constant.