Table 1 Covalent strategies for nucleic acid Conjugation on the surface of nanomaterials

Covalent conjugation

Amide bonds

Dehydration synthesis between amino and carboxyl groups

421.7 ± 8.4

Room temperature

EDC: pH 4.5–5

Sulfo-NHS: pH 5–6(react with EDC)

Sulfo-NHS: pH 7.2–7.5(react with amine)

EDC: 1.22 CNY/mg (Thermo Scientific™)

Sulfo-NHS: 8.76 CNY/mg (Thermo Scientific™)

O-Acyl isourea

intermediate/R-COOH

MNPs, Au@graphene NPs,

QDs,

UCNPs

[23,24,25,26,27]

Thioether bonds

Sulfuralcohol/mercapto group adds across multiple bonds in unsaturated compounds

713.3 ± 1.2

Room temperature

pH 6.5–7.5

SMCC: 45.94 CNY/mg (Thermo Scientific™)

Maleic acid/Michael addition reaction: Irreversible C-N bond

UCNPs, SiNPs, Ag@SiO₂,

[28,29,30,31]

Disulfide bonds

The bond between sulfur atoms in the form of -S–S- formed by the oxidation of two -SH groups

425.3

Room temperature

pH 7.0–8.0

SPDP: 67.78 CNY/mg (Thermo Scientific™)

Hydrolysis of the NHS ester

AgNPs, AuNPs,

QDs

[32,33,34]

Au–S/Ag–S/Pt–S

High affinity of sulfhydryl on the surface of noble metal nanomaterials

Au–S:

418 ± 5

Ag–S:

216.7 ± 4.6

Pt–S:

55 ± 4.8

Depends on the conjugation method

5'-Thiol Modification of Oligonucleotides: 280 CNY/2OD (Sangon Biotech (Shanghai))

–

AuNPs, AuNP@Pt, AgNPs

[35,36,37]

Schiff base

Chemical compounds (imines) bearing a hydrocarbyl group on the nitrogen atom R₂C = NR′ (R′ ≠ H)

602 ± 25

Room temperature

pH 6.0–8.0

Glutaraldehyde: 11.31 CNY/ml (Sigma-Aldrich)

5'-Amine Modification of Oligonucleotides: 105 CNY/2OD (Sangon Biotech (Shanghai))

Only single component on glutaraldehyde/Michael addition reaction: Irreversible C-N bond

Fe₃O₄@PDA NPs,

SiNPs

[38, 39]

Click Chemistry

A highly specific and selective chemical ligation method based on carbon-heteroatom bond (C-X-C) linkage

944.8 ± 0.1

Room temperature

pH 7.0–8.5

DBCO-PEG4-NHS ester: 720 CNY/mg (MCE)

5'-Azide Modification of Oligonucleotides: 280 CNY/2OD (Sangon Biotech (Shanghai))

5'-DBCO Modification of Oligonucleotides: 350 CNY/2OD (Sangon Biotech (Shanghai))

–

AuNPs, UCNPs,

SiNPs

[40,41,42]