Aunps

HS-MEG-OH and HS-MEG-COOH were synthesized based on previous procedures [5 (link),11 (link)]. Anhydrous magnesium sulphate, sodium thiosulfate, sodium carbonate, sodium iodide, sodium chloride, and absolute ethanol were obtained from the University of Toronto (Toronto, ON, Canada). Other organic solvents (methanol, ethyl acetate, hexane, dichloromethane, and acetonitrile) were analytical grade and from Sigma–Aldrich (Darmstadt, Germany). T-butyl acrylate, hydrogen peroxide, zinc, trifluoroacetic acid, β-mercaptoethanol, N-hydroxysuccinimide (NHS), 1-(3-(dimethylamino)propyl)-3-ethylcarbodiimide hydrochloride (EDC), and ethanolamine were purchased from Sigma–Aldrich (Darmstadt, Germany). Chemicals were used without further purification. Ammonium hydroxide (NH₄OH) and N-Benzyltrimethylammonium hydroxide (40% in methanol w/w) were purchased from Fisher Scientific (Ottawa, Canada). AuNPs (5 nm diameter, OD 1, stabilized suspension in 0.1 mM phosphate-buffered saline (PBS), reactant free) were purchased from Sigma–Aldrich (Darmstadt, Germany). Aqueous solutions were prepared using Milli-Q water (18.2 MΩ.cm).
The lyophilized aptamer against P. aeruginosa (5’-CCC CCG TTG CTT TCG CTT TTC CTT TCG CTT TTG TTC GTT TCG TCC CTG CTT CCT TTC TTG-3’, with a 3’ amino modification) was purchased from Generi Biotech (Hradec Králové, Czech Republic). The aptamer sequence follows these cited works [12 (link),13 (link),14 (link),15 (link),16 (link),17 (link),18 (link)]. A 100 μM stock solution of the lyophilized aptamer was prepared in DNase-free TE buffer (10 mM Tris-HCl, 1 mM EDTA, pH 8.0). This stock solution was divided into 100 μL aliquots and stored at −20 °C. Before functionalizing the gold electrodes with aptamer, an aliquot was diluted with Milli-Q water to a concentration of 5 μM. The secondary structure of the aptamer was analyzed with OligoAnalyzer Tool software (Integrated DNA Technologies, Coralville, IO, USA) and the results are reported in the Supplementary Material (see Supplementary Material, Section S1).
PBS was used as a binding buffer and was prepared with 137 mM NaCl, 2.7 mM KCl, 10 mM Na₂HPO₄, and 1.8 mM KH₂PO₄ at pH 7.4. A 0.22 μm membrane (Merck-Millipore, Darmstadt, Germany) was used to filter every solution. Pseudomonas aeruginosa PAO1 was provided by the National Collection of Agricultural and Industrial Microorganisms (Budapest, Hungary) and Lactococcus acidophilus LA-5 was kindly supplied by C. Hansen (Hørsholm, Denmark). Escherichia coli DH5α and Staphylococcus aureus KR3 were purchased from the University of Toronto Medstore (Toronto, ON, Canada). Whole UHT cow’s milk (3.5% fat) was bought from LIDL (Bratislava, Slovakia) and from Walmart (Toronto, ON, Canada).

AuNPs with different sizes were
purchased from Millipore Sigma. NaCl (NaCl, purity of >99%) was
purchased
from ThermoFisher. Aptamers (Table S1),
T1,^{26 (link)} T2,^{26 (link)} BT,^{19 (link)} and AT,^{32 (link)} were purchased
from IDT Co, which is specifically used to detect tau. The scrambled
aptamer, which has no affinity to tau, was also purchased from IDT
Co. Deionized water was used to prepare all of the solutions. Recombinant
tau was obtained from Abcam.

The 5 nm and 10 nm AuNPs were purchased from Sigma-Aldrich (Johannesburg, South Africa). The AuNPs were filtered and stored in sterile 50 mL tubes to ensure that no contamination could occur.

The nanowire growth procedure is similar to those reported in the previous studies.^[46, ^47] Gold nanoparticles (AuNPs, Sigma‐Aldrich, the average diameter of ≈20 nm) were used as catalysts dispersing on silicon wafers with a 300 nm thick thermal oxide layer. Boron‐doped p‐type SiNWs were synthesized at 470 °C for about 20 min by using 2.5 sccm Si₂H₆ (Matheson Gas Products, 99.998% Purity) as reactant gas, 0.25 sccm B₂H₆ (100 ppm, diluted in H₂) as a p‐type dopant, and 7.0 sccm H₂ as the carrier gas. The wafer on which silicon nanowires and 10–20 µL triethoxy (3‐succinate propyl) silane (TESPSA, 95%, J&K) were grown was placed in a sealed container which was then heated at 120 °C for 2 h. After the vapor modification, modified SiNWs were transferred to a 1.4 cm × 1.8 cm silicon substrate with a 1000 nm thick thermal oxide layer. The electrode patterns were defined by a standard UV lithography (BG‐401A, China electronics technology Group Corporation). After the etching of SiNWs with a buffered HF solution (40% NH₄F:40% HF, 7:1) to remove the oxide shell, 8 nm Cr and 80 nm Au were deposited through thermal evaporation (ZHD‐300, Beijing Technol Science) to form metal electrodes. A 30 nm thick SiO₂ protective layer was then deposited through electron beam thermal evaporation (TEMD‐600, Beijing Technol Science) in order to passivate the contact interface. After lift‐off with acetone, the surface‐modified SiNW FET devices were obtained.