Abstract
Nowadays, high-resolution imaging techniques are extensively applied in a complementary way to gain insights into complex phenomena. For a truly complementary analytical approach, a common sample carrier is required that is suitable for the different preparation methods necessary for each analytical technique. This sample carrier should be capable of accommodating diverse analytes and maintaining their pristine composition and arrangement during deposition and preparation. In this work, a new type of sample carrier consisting of a silicon wafer with a hydrophilic polymer coating was developed. The robustness of the polymer coating toward solvents was strengthened by cross-linking and stoving. Furthermore, a new method of UV-ozone cleaning was developed that enhances the adhesion of the polymer coating to the wafer and ensures reproducible surface-properties of the resulting sample carrier. The hydrophilicity of the sample carrier was recovered applying the new method of UV-ozone cleaning, while avoiding UV-induced damages to the polymer. Noncontact 3D optical profilometry and contact angle measurements were used to monitor the hydrophilicity of the coating. The hydrophilicity of the polymer coating ensures its spongelike behavior so that upon the deposition of an analyte suspension, the solvent and solutes are separated from the analyte by absorption into the polymer. This feature is essential to limit the coffee-ring effect and preserve the native identity of an analyte upon deposition. The suitability of the sample carrier for various sample types was tested using nanoparticles from suspension, bacterial cells, and tissue sections. To assess the homogeneity of the analyte distribution and preservation of sample integrity, optical and scanning electron microscopy, helium ion microscopy, laser ablation inductively coupled plasma mass spectrometry, and time-of-flight secondary ion mass spectrometry were used. This demonstrates the broad applicability of the newly developed sample carrier and its value for complementary imaging.
Highlights
High-resolution imaging techniques are often applied sequentially to complement each other and facilitate a comprehensive understanding of physical, chemical, and biological phenomena
The two main effects that cause an inhomogeneous distribution of analytes deposited from suspensions on a solid surface are (i) the so-called “coffee-ring effect,” which takes place when suspended particles in a solution are carried to the outer edge of a spot after deposition due to the capillary flow in a drying sample[6,7,8] and (ii) the presence of contaminants that adhere to the carrier surface and render it hydrophobic.[3,4,5]
To meet the challenge of hydrophobic compounds adhering to the sample carrier surface, we developed the new UV-ozone cleaner “PULC-120.”
Summary
High-resolution imaging techniques are often applied sequentially to complement each other and facilitate a comprehensive understanding of physical, chemical, and biological phenomena. The two main effects that cause an inhomogeneous distribution of analytes deposited from suspensions on a solid surface are (i) the so-called “coffee-ring effect,” which takes place when suspended particles in a solution are carried to the outer edge of a spot after deposition due to the capillary flow in a drying sample[6,7,8] and (ii) the presence of contaminants that adhere to the carrier surface and render it hydrophobic.[3,4,5] Organic molecules adhered to the surface change the chemical and physical properties of the surface. The suggested sample carrier can accommodate a wide variety of analytes (e.g., NPs from suspensions, cells, biofilms, tissue sections, thin sections, etc.), undergo different preparation steps, and, allows the straightforward implementation of complementary imaging studies
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