Covalent Bonding and Coulomb Repulsion-Guided AuNP Array: A Tunable and Reusable Substrate for Metabolomic Characterization of Lung Cancer Patient Sera

Abstract

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) has gained increased attention in the metabolic characterization of human biofluids. However, the stability and reproducibility of nanoparticle-based substrates remain two of the biggest challenges in high-salt environments. Here, by controlling the extent of Coulomb repulsion of 26 nm positively charged AuNPs, a homogeneous layer of covalently bonded AuNPs on a coverslip with tunable interparticle distances down to 16 nm has been successfully fabricated to analyze small biomolecules in human serum. Compared with the self-assembled AuNP array, the covalently bonded AuNP array showed superior performances on stability, reproducibility, and sensitivity in high-salt environments. The stable attachment of AuNPs maintained a detection reproducibility with a RSD less than 12% and enabled the reusability of the array for 10 experiments without significant signal deterioration (<15%) and carryover effects. Moreover, the closely positioned AuNPs allowed the coupling of photoinduced plasmons to generate an enhanced electric field, which promotes the generation of excited electrons to facilitate the desorption/ionization processes instead of the heat dissipation, thus enhancing the detection sensitivity with detection limits down to the femtomole level. Combined with machine learning methods, the AuNP array has been successfully applied to discover seven biomarkers for differentiating early-stage lung cancer patients from healthy controls. It is anticipated that this simple approach of developing robust AuNP arrays can also be extended to other types of NP arrays for wider applications of SALDI-MS technology.

Self-Assembled Hyperbranched Gold Nanoarrays Decode Serum United Urine Metabolic Fingerprints for Kidney Tumor Diagnosis

“…Compared to hyperbranched AuNPs, closely packed HyBrAuNAs generated abundant hot spots within the nanoscale gap, which was reflected by the plasmonic redshift of UV–vis absorbance, presenting a strong plasmonic coupling band at 900 nm (Figure b). Such plasmonic hot spots efficiently enhanced the EM field as proved by EM field simulation (Figure a), which may induce more photoexcited electrons for ion desorption. , Moreover, the confined heat on the surface of HyBrAuNA could assist in desorbing the analytes . Taken together, the HyBrAuNA possesses excellent EM field enhancement and photothermal conversion capability, which is beneficial to facilitate the desorption and ionization of analytes.…”

“…Such plasmonic hot spots efficiently enhanced the EM field as proved by EM field simulation (Figure 2a), which may induce more photoexcited electrons for ion desorption. 51,52 Moreover, the confined heat on the surface of HyBrAuNA could assist in desorbing the analytes. 26 Taken together, the HyBrAuNA possesses excellent EM field enhancement and photothermal conversion capability, which is beneficial to facilitate the desorption and ionization of analytes.…”

Serum Lipidomic Fingerprints Encode Early Diagnosis and Staging of Lung Cancer on a Novel PbS/Au-Layered Substrate

“…A series of common metabolites, such as glucose, acetylcholine, cytosine, and lecithin, were further used as model analytes to determine the limit of detection (LOD). 18 As shown in Figures 3d and S7a−d, the LODs and linearities recorded in the positive ion mode were as follows: acetylcholine LOD = 37 fmol, R 2 = 0.9988; lecithin LOD = 220 fmol, R 2 = 0.9959; cytosine LOD = 1160 fmol, R 2 = 0.9935; glucose LOD = 2337 fmol, R 2 = 0.9921. The detection reproducibility of the optimized PbS/ Au-layered substrate was also determined.…”

“…Therefore, PbS QDs with 0.62 eV in bandgap and AuNPs with 25.1 nm in diameter were ultimately adopted as the optimal assembly to fabricate PbS/Au-layered nanostructures for further studies. A series of common metabolites, such as glucose, acetylcholine, cytosine, and lecithin, were further used as model analytes to determine the limit of detection (LOD) . As shown in Figures d and S7a–d, the LODs and linearities recorded in the positive ion mode were as follows: acetylcholine LOD = 37 fmol, R 2 = 0.9988; lecithin LOD = 220 fmol, R 2 = 0.9959; cytosine LOD = 1160 fmol, R 2 = 0.9935; glucose LOD = 2337 fmol, R 2 = 0.9921.…”

“…AuNPs were synthesized using a seed-mediated successive reduction method based on our previous studies. , The 5 nm AuNP seeds were prepared by first mixing 5.0 mL of 0.75 mM potassium tetrachloroaurate (KAuCl 4 ) solution and 5.0 mL of 3.75 mM sodium citrate solution. Then, 5.0 mL of a 3 mM sodium borohydride (NaBH 4 ) solution was added dropwise upon stirring.…”