Figure 9. (a) Purity (A620/A280) and (b) APC and P-PC yield recovered
after VFD-ATPS processing at various speeds of
rotation28, (c) conversion levels of substrates
increase dramatically by swapping from non-covalent to covalent
attachments, (d) optimized symmetrical amine-glutaraldehyde cross-linker
for β-glucosidase applied for phosphodiesterase and alkaline
phosphatase, with excellent stability after processing over ten hours,
(e) β-glucosidase solution recycled, with the last sample tube having a
similar substrate transformation to the first, (f) >20%
catalytic activity for enzyme-immobilized tubes without buffer after
being stored for one month56, (g) optimization of
processing parameters (ratio of biomass to methanol, catalyst
concentration, reaction time and rotational speed in rpm) for
VFD-mediated dry biomass processing in confined mode. (h) TEM image
(inset 10 nm scale bar), (i) SEM image, and (j) AFM image of
P4C6-carboplatin host-guest vesicles after VFD processing, with (k)
collapsed vesicle’s sectional height profile and host-guest complex
elemental mapping with energy-filtered transmission electron microscopy
for (l) unfiltered, (m) carbon, and (n) platinum49.
(a-b) Reproduced with permission28. Copyright 2016,
American Chemical Society. (c-f) Reproduced under the terms of the CC BY
3.0 license56. Copyright 2016, Royal Society of
Chemistry. (g) Reproduced with permission53. Copyright
2018, Elsevier. (h-n) Reproduced under the terms of the CC BY 4.0
International license49. Copyright 2015, Springer
Nature.
Recently, aggregation induced-emission luminogens (AIEgens) with high
emission efficiency in the aggregated state, excellent photo-stability,
and increased sensitivity have become one of the most promising
nanoprobes for both material and process characterizations due to their
flexibility, versatility, and robustness when compared to other
strategies. The most frequently used approach to preparing AIEgen
particles is precipitation. Without proper mixing under shear, AIE
particles will be distributed in various sizes, affecting their ultimate
brightness and applications. In the inaugural attempt for VFD-mediation
of AIEgen size, controlling the size and shape of AIEgens was possible,
impacting their fluorescence (FL) properties57. By
increasing both concentration and rotational speed during the
preparation of a particular AIEgen, tetraphenylethylene (TPE), the
particle size was controlled and significantly reduced, with the smaller
particles increasing the brightness. The ability of the VFD to produce
AIEgens <10 nm in size with tunable FL intensities directly
from a 90% solvent/antisolvent (SA) ratio at the VFD rotational speed
of 5000 rpm is shown in Figure 10. In traditionally prepared TPE
particles, a 40-times increase in the fluorescent maxima had been
observed at the SA ratio of 95% compared to that of TPE particles
prepared at the SA ratio of 80%. At SA ratios < 80%, the
associated emissions had been zero. Surprisingly, it was found that
VFD-derived solutions of TPE particles were fluorescent at the SA ratios
< 80% (down to the SA ratio = 40%). At constant rotation
speeds above 1000 rpm, the SA ratio increased to fluorescent maxima and
maximum relative intensity. The highest maximum relative intensity for
VFD-derived TPE particles was about 190 times greater for the SA ratio
and rotation speed of 90% and 5000 rpm, respectively. Although other
approaches, including multi-channel and microfluidic methods, had been
unable to produce AIEgens <80 nm in size, use of the VFD
provides a unique strategy to tune the size and control the FL property
of AIEgens, which are important properties for different applications.
As an advantage of size reduction, the direct diffusion of NPs within a
cell or in a single-celled organism opens new opportunities for
biological and material studies.
In another study, TPE-2BA AIEgen, a derivative of tetraphenylethylene
with two boronic acid groups, was physically coupled with a commercially
available hyperbranched polymer (HBP; bis-MPA polyester-64-hydroxyl;
generation 4) using VFD58. Significant differences in
FL intensity were found for the AIE–HBP (HBP concentration = 1 mM) at
different SA ratios, as shown in Figure 10. The FL intensity increased
32-fold with the SA ratio = 90% compared to the SA ratio of 40%.
Negligible changes in particle size in the VFD-driven AIE-HBP particles
were reported compared to those prepared without VFD. The formation of
AIE-HBP under shear stress increased AIE molecules’ penetration within
the HBP structure, leading to significantly brighter AIE-HBP particles.
It was reported that at the SA ratio = 90%, the average particle size
for the traditionally prepared AIE-HBP was approximately 150 nm, with a
relative FL intensity of 38 times greater than that of TPE-2BA alone.
When the VFD was used, the particle size of the AIE-HBP was reduced to
approximately 80 nm, and the relative FL intensity became 73 times
greater. The formation of a smaller AIE-HBP complex containing more AIE
molecules within the HBP molecule structure might be the reason for that
observation. The authors concluded that, with the employment of a VFD,
it was possible to form an AIE-HBP complex less than 100 nm in size
under optimized conditions. This later resulted in the fabrication of
fluorescent hydrogels with enhanced mechanical properties, and no sign
of failure was observed in the hydrogel containing AIE-HBP (1 mM) over
800% strain.