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Page 12 of 34 Bai et al. Soft Sci 2023;3:40 https://dx.doi.org/10.20517/ss.2023.38

[162]
remove the oxide shell [Eq. (3)] , resulting in a significant reduction in contact angle from 128° to 27°,
and selective wetting of the unoxidized portion of the printed composite using Cu nanofillers in Galinstan
microdroplets to achieve chemical sintering [Figure 4B iii].

Chemical transformation is more than just a chemical reaction. The surface of LMNPs can also be further
enhanced in terms of structural stability and multi-functionalization by modifying chemical groups. For
example, the modification of thiols, such as 1-butanethiol and benzenethiol, can effectively prevent LMNPs
[163]
from oxidation . The modification of surfactants, such as Pluronic 127 (PF127), can enhance particle
mechanical stability and prevent particle aggregation . The modification of polyfunctional substances,
[164]
such as polydopamine, can further modify other functional substances through electrostatic adsorption and
chemical bonding . Furthermore, modifying substances with conjugation potential, such as
[137]
[163]
4-mercaptopyridine, can enhance the electrical conductivity of LMNPs .
Sensing information detection and acquisition
Gallium oxide encapsulated on the surface of gallium NPs can change the resistance by gaining and losing
electrons and act as a detection sensor for some typical redox chemicals. For example, based on the electron
donor-acceptor mechanism, the reducing gas H molecules lose electrons after the reaction, and the free
2
electrons are captured by gallium oxide, leading to a gradual decrease in the resistance of n-type samples
[Figure 4B iv]. Conversely, the oxidizing gas NO molecules take away electrons from the gallium oxide,
2
which leads to the gradual increase of the resistance of the n-type sample, thus achieving the accurate
resistance change measurement [Eq. (4)] . Meanwhile, for different crystalline phases of gallium oxide, it
[165]
was found that monoclinic phase gallium oxide can be produced in dimethyl sulfoxide (DMSO), while
oblique crystalline phase gallium oxide is produced in water. As rhombic gallium oxide is not conducive to
gas sensing, this makes gallium NPs in DMSO more sensitive than the gas in water .
[165]

By ultrasonic nitriding at room temperature, GaN is formed on the surface of GaOOH crystals on the
outside of LM microparticles [Eq. (5)] , and the LM microparticles are rapidly transformed into LMNPs.
[99]
At the same time, part of GaOOH and GaN are detached, and non-spherical particles consisting of
orthorhombic α-GaOOH embedded in the domains of the hexagonal GaN structure are formed. As a 3.4 eV
wide bandgap semiconductor material, gallium nitride has photoluminescence properties, which makes
gallium NPs also have photoluminescence properties [Figure 4B v]. Since nitride has an adsorption effect on
some organic substances, such as bovine serum albumin, the gallium NPs encapsulated with gallium nitride
can detect its concentration by the burst effect to achieve accurate biosensing.

Other chemical bonds can be modified on the surface of gallium NPs, such as modifying sulfur bonds (-SH)
to form gallium-sulfur covalent bonds [Eq. (6)] to connect gallium NPs with polymeric organic matter
[100]
for specific biosensing. For example, based on the nature of gallium surface plasmon resonance, the 12-mer