Surface Modification of Liquid Metal with p-Aniline Derivatives toward Bioapplications: Biosensing as an Example

Abstract

It is a long-lasting research topic to avoid the formation of oxidation layers on gallium-based liquid metals. This study has developed a simple general method for modification of the eutectic gallium−indium (EGaIn) surface with p-aniline derivatives to introduce a monolayer of organic molecules with versatile functional groups. The binding affinity of carboxylic acid groups, amine groups, or thiol groups with EGaIn is in the order SH > NH 2 > COOH. For the first time, it is evidenced that both NH 2 and SH groups can coexist on the EGaIn nanoparticle surface with the binding affinities of 30 and 70%, respectively. The formation of these organic molecules on the EGaIn surface antioxidizes and thus stabilizes the EGaIn nanoparticles, while increasing the conductivity of EGaIn significantly. The resulting EGaIn nanoparticles have very good distribution in both ethanol and aqueous solutions and rich surface chemistry, making them suitable for the following attachment of biomolecules such as aptamers, antibodies, or enzymes for biomedical applications. As an example, the EGaIn surface is successfully modified with p-aminobenzoic acid followed by the attachment of an insulin aptamer, which can be used for the electrochemical detection of insulin with the lowest detectable concentration limit of 1 pM. This study reveals the modification of EGaIn nanoparticles with p-aniline derivatives with versatile functional groups to antioxidize EGaIn in a biological environment, opening a door for gallium-based liquid metals toward biomedical applications.

Ligand Mediation for Tunable and Oxide Suppressed Surface Gold‐Decorated Liquid Metal Nanoparticles

“…The anti‐mouse IgG antibody labeled fluorescein isothiocyanate tag (antibody‐FITC) has been proven to be able to be immobilized on the EGaIn‐PABA, as the amine groups on the antibody can form an amide bond with the carboxylic acid group with the help of N ‐(3‐dimethylaminopropyl)‐ N ′‐ethylcarbodiimide hydrochloride‐1/ N ‐hydroxysulfosuccinimide sodium salt (EDC/NHS). [ 18 ] Therefore, the same antibody‐FITC molecules were incubated with EGaIn‐PABA@Au to investigate if there are free carboxylic acid groups on EGaIn‐PABA@Au. Compared with pure EGaIn‐PABA, EGaIn‐PABA@Au showed a significant increase in the fluorescent intensity after the modification of antibody‐FITC by covalent bonding based on EDC/NHS coupling (Figure 2d).…”

“…Among all EGaIn‐ p ‐aniline‐R@Au nanodroplets, EGaIn‐PPD@Au had the highest electric conductivity and the best electron transfer ability, which aligns with the electrochemistry result before incubation in HAuCl 4 . [ 18 ]…”

“…Among all EGaInp-aniline-R@Au nanodroplets, EGaIn-PPD@Au had the highest electric conductivity and the best electron transfer ability, which aligns with the electrochemistry result before incubation in HAuCl 4 . [18] The Nyquist figures of EGaIn, EGaIn@Au, and EGaIn-PABA@Ga 2 O 3 showed the largest second radius, suggesting conductivity improvement after modification with p-aniline derivatives and AuNPs. [44] Figure 3d shows the electrochemical performance of different EGaIn-p-aniline-R@Au in H 2 SO 4 solution.…”

“…We showed that such molecules significantly enhanced stability and electrical conductivity while introducing functional groups to the surface of EGaIn nanoparticles. [ 18 ] Biomolecules such as antibodies or aptamers were incorporated into EGaIn, and p ‐aminobenzoic acid‐modified EGaIn were successfully used for insulin biosensing. However, the need for high electrical conductivity for such biosystems still raises the prospect of exploring other methods for reducing the native oxides even further and gain more surface versatility altogether to expand the biomedical applications.…”

Printable biosensors towards next-generation point-of-care testing: paper substrate as an example

“…Liquid metal modified with small organic molecules demonstrates potential as the bioink for printable biosensors. 184…”