Cypher s instrument

Lyophilized samples were imaged in non-contact mode with a Cypher S instrument (Asylum Research, Santa Barbara, CA, USA) at 1–2 Hz line-scanning rate in air using a silicon cantilever (OMCL AC-160TS, Olympus, Tokyo, Japan) and oscillated at its resonance frequency (typically 300–320 kHz). Temperature during the measurements was 29 ± 1 °C. Images were analyzed by using the built-in algorithms of the AFM driving software (IgorPro, WaveMetrics Inc., Lake Oswego, OR, USA). AFM amplitude-contrast images are shown in this paper. To determine height variations, height-contrast data were used.

For imaging PBNP complexes, two-fold diluted samples were applied onto poly-L-lysine (PLL)-coated surfaces. PLL-coated substrate surface was prepared by pipetting 100 μL of PLL (0.1% w/v) onto freshly cleaved mica, followed by incubation for 20 min, repeated rinsing with purified water, and drying with a stream of high-purity nitrogen gas. AFM images were collected in noncontact mode with a Cypher S instrument (Asylum Research, Santa Barbara, CA, USA) at 1 Hz line-scanning rate in air, using a silicon cantilever (OMCL AC-160TS, Olympus, Tokyo, Japan) oscillated at its resonance frequency (270–300 MHz). Temperature during the measurements was 25 ± 1°C. AFM amplitude-contrast images are shown in this paper. The filter used on the images enhances the details of the amplitude contrast images (mud). AFM images were analyzed by using the built-in algorithms of the AFM driver software (Igor Pro, Wave Metrics Inc., Lake Oswego, OR, USA). Particle statistics was done by analyzing a 2 μm × 2 μm height-contrast image with (n = 178) particles. Maximum height values were taken as the height of particles, and rectangularity was calculated as the ratio of the particle area to the area of a nonrotated inscribing rectangle. The closer a particle is to a rectangle, the closer this value is to unity.

AFM
topographic images were collected using a Cypher S instrument (Asylum
Research, Oxford Instruments) operating in tapping mode. During the
operations, silicon tetrahedral tips were used, mounted on rectangular
30 μm cantilevers, purchased from Olympus (AC240TS, Oxford Instruments).
The probes had a nominal spring constant of 2 N/m and driving frequencies
of 70 kHz. To perform the analysis, samples were deposited on freshly
exfoliated muscovite mica (Ted Pella, Inc.). After 5 min from the
moment of deposition, mica dishes were washed with 1 mL of ultrapure
water and dried under a gentle nitrogen flow.