Dr. Hiroshi Masuhara is one of the most reputable Japanese chemists, awarded The Purple
Medal (紫綬褒章) and The Order of Sacred Treasure, Gold Ray with Double Neckless(瑞宝中綬章), honored internationally The Porter Medal (corresponding to Nobel Prizein photochemistry), and Academicians of The Royal Academy of Belgium and National
Academy of Sciences India. This is due to his pioneering study on nano/micro molecularsystems exploring their new photochemical and photophysical phenomena by developing
time-resolved spectroscopy, imaging, and manipulation methods and by elucidating theirdynamics and mechanism. He has opened new interdisciplinary area of molecular photoscience, whose results are published as ~560 papers, ~120 reviews, and ~20 books. His
pioneering works have attracted many young researchers and graduate students. Now 63
doctors graduated/educated from Masuhara Laboratory/Project and 40 researchers
coached in Masuhara Project are working in the relevant areas of molecular photo-science
as professors and distinguished researchers in 10 countries including Taiwan.
This long developing academic research by Dr. Masuhara before shifting to NCTU in2008 is summarized as “Laser Nano Chemistry: Methodology and Molecular NanoDynamics”. This consist of 3 parts.

Since 2015 we have been intensively studying optical trapping dynamics andmechanism of nanoparticles (NPs) at solution interfaces. In 2020 and 2021, we could
not attend international conferences, could not organize our Annual Summer Courseand Workshops, could not invite foreign professors to DAC Colloquium andlaboratory seminars, and many visiting plans including Japanese super science highschool students to our campus were canceled. We have been keeping international
contact through online, and fortunately we resume foreign travel and join themeetings from this September. I have had several invited lectures in Japan and visited
our collaborator, Profs. Johan Hofkens and Roger Bresoli-Obach in Katholieke
Universiteit Leuven (KULeuven) in Belgium. Also I attended the Annual Meeting ofJapanese Photochemistry Meeting and three students joined the Autumn Meeting ofJapan Society of Applied Physics with me. We have published 5 papers and theyreceived much attention in our research fields.
The first subject of this year is on “Optically Evolved Assembling and Swarming”
of gold NPs at glass/solution interface. The trapped gold NPs periodically align insideand outside the focus, scatter the trapping laser, and attract many gold NPs. The
scattering direction is perpendicular to laser polarization, giving a dumbbell-shaped
assembly. The NPs at both sides of the focus are fluctuating like a group of bees, sothat we named its behavior “Swarming”. This year we study on swarming
morphology control and nature of optical binding at the central part. Particularly wehave made clear optical binding takes place not only inside the irradiated area but also
outside the focus. This is because the trapping laser is extremely intense and even thescattered light outside the irradiated area is enough strong to achieve optical binding.
This is published in Nature Communication.
The second subject is on “Optically Evolved Assembling” of polystyrene (PS) NPs
at solution interface. The trapped NPs in the focus scatter the trapping laser,expanding the optical potential to the outside along the interface. A single disc-likelarge assembly of the NPs is formed, reaching a few ten micrometers. Utilizing dual
objective lens microscopes enables us the three-dimensional analysis of thephenomena. This trapping assembling is also coupled with resonance effect by which
optical force is enhanced, leading to new phenomenon and application. We
demonstrated that resonance effect results in interesting behavior on particle
assembling dynamics and increased sensitivity to surrounding chemical condition.
These are the results obtained ahead of the world.
The third subject is on “Optically Evolved Assembling Condensation” of protein at
air/solution interface. The trapped protein is distributed from the focus to the outside
reaching a few ten micrometers in diameter and depth. The concentration is higher
than super-saturation but still concentrated densely by a few times. The dynamics and1.

mechanism of this large assembly is being studied by synchronous transmission andfluorescence imaging, Raman microscopy, and three-dimensional tracking ofindividual fluorescent PS particles added as a probe. As an application of opticaltrapping to protein solution, we succeeded in publishing Chemical Communication on
structural nature of its amyloid formation.
1. The primeval optical evolving matter: Optical binding inside andoutside the photon beam
Optical binding has recently gained considerable attention because it enables thelight-induced assembly of many-body systems; however, this phenomenon has onlybeen described between directly irradiated particles. We have demonstrated that
optical binding can occur outside the focal spot of a single tightly focused laser beam.
By trapping at an interface, we assemble up to three gold nanoparticles with a linear
arrangement which fully-occupies the laser focus. The trapping laser is efficientlyscattered by this linear alignment and interacts with particles outside the focus area,generating several discrete arc-shape potential wells with a half-wavelength
periodicity. Those external nanoparticles inside the arcs show a correlated motion not
only with the linear aligned particles, but also between themselves even both are notdirectly illuminated. We propose that the particles are optically bound outside thefocal spot by the back-scattered light and multi-channel light scattering, forming a
dynamic optical binding network. at room temperature ultimately.
2. Unraveling the three-dimensional morphology and dynamics of the optically
evolving polystyrene nanoparticle assembly using dual-objective lensmicroscopy
Dynamically fluctuating assembly is prepared by trapping microparticles or
nanoparticles at an interface. This phenomenon was previously described for 500 nm
PS NPs optically trapped at water/glass interface, yielding a single disk-like assembly,
which size is much larger than the focal volume. We use a dual-objective lensmicroscope to study the three-dimensional shape and dynamics of such disk-like
assembly. The higher resolution of this system, together with fast image acquisition(80 fps), rendered novel insights (e.g., particle fluctuation, assembly shape,
interparticle distance, and so on), which could not be resolved using a conventional
inverted microscope. These new insights will help to unravel the basis of this not yet
fully understood “optically evolved phenomena,” which has a large potential indifferent research fields such as optical trapping, soft matter, and colloidal chemistry.
3. The Optical Absorption Force Allows Controlling Colloidal AssemblyMorphology at an Interface
Gaining control on particle–particle interactions and in this way on their self1.

-assembled structures is essential for colloidal and material sciences. Currently,
different strategies are described to achieve such control, however, all of them lackthe spatiotemporal resolution required at the microscale. The potential of combining
optical trapping and resonant photoexcitation for modifying particle–particle
interactions and subsequent assembling of dye-doped particles at the solution
interface is demonstrated. The particle assemblies prepared by non-resonant 1064 nm
optical trapping undergo morphology changes after resonant photoexcitation of theembedded dye molecules. Depending on the physicochemical properties of interface,quick hexagonal close packing (HCP)-rearrangement or explosive dispersion ofassemblies is observed at air/solution (A/S) and glass/solution interfaces, respectively.
By contrast, by resonant photoexcitation only, the dispersed dye-doped particles arepushed toward the A/S interface, followed by association to yield HCP-structured
assemblies. The results are rationalized by considering the optical absorption force
coupled with other non-optical forces (e.g., capillary force, dipole–dipole interaction,or electrostatic repulsion) at the solution interface. Due to the inherent spatiotemporal
properties of light and electronic transition of materials, absorption force is a uniqueelement to control and modify the structural order of particle assemblies at interfaces
4. Chemical Control Over Optical Trapping Force at an Interface
So far, the optical trapping potential is controlled by tuning the physical conditions ofthe system. We study that the induced optical force or optical potential is controlled,
by an external chemical stimulus. The key to realize this is to design an opticaltrapping condition in conjunction with resonant excitation, the so-called opticalresonance effect. For this purpose, phenalenone, a well-known triplet photosensitizer,
is embedded inside polystyrene particles. The optical resonance effect is achieved
through a two-laser system; a 405 nm widefield laser to excite the phenalenone
molecules to T1 state and a 488 nm trapping laser to induce the T1–Tn–T1 resonancecycle. Thus, the triplet state is mainly responsible for the optical force enhancement.
Since oxygen is an excellent triplet quencher, the triplet populations, and hence, theoptical force is controlled by changing the dissolved oxygen concentration. The
results presented pave the way to chemically control the optical force through opticalresonance with promising applications in several research fields ranging from physics
to biology.
5. Structural region essential for amyloid fibril formation in cytochrome celucidated by optical trapping
Amyloid fibril formation of cytochrome c is spatially and temporally controlled with a
combined method of disulfide bond cross-linking of cysteine-introduced variants andoptical trapping, identifying that the structural change in the region containing Ala83
is essential for the amyloid fibril formation.
1.

The MOST-FWO Bilateral Corporation Program on “Three-Dimensional
Dynamic Observation and Analysis of Optically Evolving Assembly ofNanoparticles and Proteins at Solution Interface”
In 2020 we proposed the program and it was approved for Jan. 1, 2021- Dec. 31,2022. The principal scientists in this collaboration are Prof. Hiroshi Masuhara ofNYCU in Taiwan and Prof. Johan Hofkens of KULeven in Belgium, respectively.
During this term we have been publishing 7 papers including Nature Communication,
Dr. Roger Bresoli-Obach stayed in NYCU for a half year, and our 6 graduate students
visited KULeuven each for 2 months. Every Monday afternoon we have the Program
Meeting by online, one student talks on his/her progress, and all members discuss on
it. To assist this corporation, finalize the activity result, and exchange our opinions, I
went to KULeuven for November 13-23 and met Profs. Johan Hofkens, Susana Rocha,and Hiroshi Fukumura, Dr. Bresoli-Obach, and several students. My activity of thistrip is summarized as follows, which are the base for the next application.

1.