Surface Modification Enabling Reproducible Cantilever Functionalization for Industrial Gas Sensors

Micro-cantilever sensors are a known reliable tool for gas sensing in industrial applications. We have demonstrated the application of cantilever sensors on the detection of a meat freshness volatile biomarker (cadaverine), for determination of meat and fish precise expiration dates. For achieving correct target selectivity, the cantilevers need to be functionalized with a cadaverine-selective binder, based on a cyclam-derivative. Cantilever surface properties such as surface energy strongly influence the binder morphology and material clustering and, therefore, target binding. In this paper, we explore how chemical and physical surface treatments influence cantilever surface, binder morphology/clustering and binding capabilities. Sensor measurements with non-controlled surface properties are presented, followed by investigations on the binder morphology versus surface energy and cadaverine capture. We demonstrated a method for hindering binder crystallization on functionalized surfaces, leading to reproducible target capture. The results show that cantilever surface treatment is a promising method for achieving a high degree of functionalization reproducibility for industrial cantilever sensors, by controlling binder morphology and uniformity.

Effects of laser spot positioning with optical beam deflection method on tapping mode and bimodal AFM

This work focuses on the importance of laser location and its effect on contact mode, tapping mode, and bimodal AFM both theoretically and experimentally. It is found that the current guidelines in the field might lead to mischaracterization of matter especially in bimodal AFM. A numerical study is done for a cantilever with its tip located at the end while interacting with two different polymers of Polystyrene (PS) and Low-density polyethylene (LDPE). Different observables are recorded at the end of the cantilever, 80% of its length, and 60% of its length. These results are verified by experiments in contact mode, tapping mode and bimodal AFM. Bimodal AFM observables are converted to energy quantities (i.e., virial and dissipated power) which are used to characterize soft matter in this field. Similar to simulation, for each of these measurements three different laser locations are selected. Finally, it is found there are certain locations on the cantilever that should be avoided for placing the laser while exciting higher eigenmodes. Hence, locating the laser around 80% of its length while performing bimodal AFM with the first and second eigenmodes on polymer surfaces can decrease phase contrast. It is concluded that: (1) contact mode AFM on stiff surfaces might not be effected by change of laser location, (2) misalignment of laser can cause up to 40% of mischaracterization in tapping mode and (3) 10% of phase contrast reduction in addition to 20% percent of reduction in amplitude oscillations in bimodal AFM. It is shown this can lead to mischaracterization of material. By positioning the laser location closer to the clamped end of the cantilever, surface indentation can occur. Although this is considered as a surface damage in soft matter imaging, it can be considered as a new capability of multifrequency AFM for surface modification.

A Theoretical Study of Deflection of AFM Bimaterial Cantilevers Versus Irradiated Position

The bimaterial cantilevers of atomic force microscopes have been widely used in chemical and bio-sensing. Due to the difference in the thermal expansion coefficients of the two layers, the cantilever is deflected and its deflections is dependent on the heat absorption from the ambient environment or the objects adsorbed on the cantilever surface. In this study, we theoretically examine the deflection of this cantilever considering different irradiated configurations of a laser beam and thicknesses of the coating layer. We show that the temperature difference between the end and the clamped position is maximized for an irradiation at the cantilever end and this difference reduces with increasing coating thickness. Especially, the maximal deflection is seen for an irradiation in the middle of the cantilever, around 0.6 of the cantilever length from the clamped position. The obtained results could help determining an irradiated configuration of laser and the coating thickness to optimize the sensitivity of the cantilevers in thermally sensing devices.

Asymmetric immobilization of antibodies on a piezo-resistive micro-cantilever surface

For cantilever-based MEMS sensors, selective chemical modification of the sensing surface is used for the detection of chemical and biological analytes.

Fundamental Study of the Micro-Cantilever for more Sensitive Surface Stress-Based Biosensor

Surface stress-based biosensors as a crucial part of micro-scale and label-free system, use free energy change, the underlying concept in any binding reaction, have been investigated extensively in recent years. In this paper, a new bi-micro-cantilever surface stress biosensor is proposed which can be used to detect cells. Some fundamental study has been done, especially for the micro-cantilever due to its crucial role in the whole system. To acquiring the optimal material for more sensitive sensor, four material, Si, SiN, AlN, PMMA(polymethylmethacrylate), were contrastively analyzed under the same conditions (loads, size, environmental factor. etc) by finite element (FE) method. This study could provide some foundation for the biosensor design and fabrication.