Dimension fastscan afm

AFM images were obtained using a Bruker Dimension FastScan AFM (Billerica, MA, USA) in knockdown mode. Optical images were obtained using a Sunwoo RX50M microscope (Yuyao, China). Transmission electron microscopy was performed with a 200 kV Talos F200S transmission electron microscope. Room-temperature Raman and PL spectra were recorded with a Horiba Raman microscope (Irvine, CA, USA) with 532 nm laser excitation. The X-ray photoelectron spectroscopy (XPS) of the samples was carried out using a Thermo Scientific Kα XPS spectrometer (Waltham, MA, USA) equipped with a monochromatic Al-Kα X-ray source.

A suspension of exosporium fragments (Section 2.4) was incubated on freshly cleaved mica (Agar Scientific) for 20 min, then washed with 10 × 1 ml of HPLC grade water (Sigma Aldrich). Samples imaged in water were used without further preparation; samples imaged in air were blown dry with filtered nitrogen. Imaging in water was performed using a Dimension FastScan AFM (Bruker) and FastScan D probes (nominal force constant and resonant frequency 0.25 N/m and 110 kHz in water, respectively) in tapping mode with a free amplitude of approximately 1.2 nm and a set point of 80–90% of this value. Imaging in air was performed using a Multimode (Bruker) or NanoWizard^® 3 (JPK) AFM in tapping mode using TESPA probes (Bruker) with a nominal force constant and resonant frequency of 40 N/m and 320 kHz, respectively. The free amplitude was approximately 8 nm and images were acquired with a set point 90–95%. In both environments, the feedback gains, scan rate, set point and Z range were adjusted for optimal image quality while scanning. Height and phase images were acquired simultaneously and processed (cropping, flattening, plane fitting) using NanoScope Analysis or JPK DP software.

The optical absorption spectra of the dispersion sample were recorded on an ultraviolet–visible spectrophotometer (V-770, JASCO). Raman spectra in the radial-breathing mode region were recorded on an inVia Raman Microscope (Renishaw) excited by 785-nm laser light. A single-monochromator micro-Raman spectrometer was employed in the back-scattering configuration. The sample dispersions were drop-casted onto a silicon wafer before the measurement. X-ray photoelectron spectroscopy (XPS) data were obtained using an ESCALAB XI + spectrometer (Thermo Fisher Scientific) using 300 W Al–Ka radiation. To exclude the substrate signals, a highly concentrated MXene dispersion was drop-coated several times onto a Si/SiO₂ wafer to form a thick MXene film (>10 nm). Atomic force microscopy (AFM) measurements were acquired using a Dimension Fastscan AFM with a NanoScope V stage controller (Bruker). The samples for AFM observation were prepared by spin-coating the Si/SiO₂ wafer with 10 µl of the MXene dispersion at 400 rpm for 60 s, followed by 1,000 rpm for 60 s and 1,600 rpm for 60 s. Scanning electron microscopy (SEM) measurements were conducted in an S-4300 (Hitachi) or an ETHOS NX5000 (Hitachi). X-ray diffraction (XRD) spectra were obtained by a SmartLab (Rigaku) through Cu Kα radiation.

Samples for atomic force microscopy (AFM) were prepared by dilution (between 1 : 200 and 1 : 20 000) of the WPI samples in 10 mM HCl and then applied on freshly cleaved mica surfaces. After drying in air, the samples were investigated using a Dimension FastScan AFM (Bruker) operating in tapping mode. FastScan A cantilevers (Bruker) were used for the experiments and the images were investigated using Nanoscope 1.5 software. Control experiments were also performed in liquid using ScanAsyst liquid + cantilevers (Bruker) operating in peak force mode. These experiments showed the same difference between the morphologies of straight and curved PNFs.

Imaging was carried out using a Bruker Dimension FastScan AFM using FastScan-D probes (Bruker—nominal k = 0.25 N/m, nominal cantilever length = 16 μm) in “Tapping Mode” (Amplitude Modulated Intermittent Contact Mode) driven at ~110 kHz with a free amplitude of ~1 nm.
All imaging of polymer envelopes (sacculi) was carried out in liquid (buffer) without drying at any point.