Bifunctional Au@Pt/Au core@shell Nanoparticles As Novel Electrocatalytic Tags in Immunosensing: Application for Alzheimer’s Disease Biomarker Detection

Abstract

In this work, bifunctional core@shell Au@Pt/Au NPs are presented as novel tags for electrochemical immunosensing.Au@Pt/Au NPs were synthesized following a chemical route based on successive metal depositions and galvanic replacement reactions from the starting AuNPs. Au protuberances growth on the surface of Au@Pt NPs allowed their easy bioconjugation with antibodies, while the high catalytic Pt surface area was approached for their sensitive detection through the electrocatalysed water oxidation reaction (WOR) at neutral pH. Moreover, the synergy between Au and Pt metals on the NP surface also lead to an increased catalytic activity, improving the sensitivity of the NP detection. Cyclic voltammetry and chronoamperometry were used for the evaluation of the Au@Pt/Au NPs electrocatalytic activity towards WOR. The chronoamperometric current recorded at a fixed potential of +1.35 V was selected as the analytical signal, allowing the quantification of Au@Pt/Au NPs at 10 13 NPs/mL levels. The optimized electrocatalytic method was applied to the quantification of conformationally altered p53 peptide Alzheimer's disease (AD) biomarker in a competitive immunoassay using magnetic bead (MB) platforms at levels as low as 66 nM. The performance of the system in a real scenario was demonstrated analysing plasma samples from a cognitively healthy subject. This novel Au@Pt/Au NPs-based electrocatalytic immunoassay has the advantage, over common methods for NP tags electrochemical detection, of the signal generation in the same neutral medium where the immunoassay takes place (0.1 M PBS pH 7.2), avoiding the use of additional and more hazardous reagents and paving the way to future integrated biosensing systems. 38 trolled synthesis, higher stability against harsh conditions, 39 higher resistance to high concentrations of substrate and a lower 40 cost [3][4][5][6] . The use of electrocatalytic NPs as labels has been ex-41 tensively studied and applied in immunosensing [7][8][9][10][11][12] , offering 42 outstanding alternatives to traditional assays. 43Among the wide variety of NPs, metallic NP labels have at-44 tracted considerable interest due to their unique red-ox and op-45 tical properties 13,14 as well as their electrocatalytic activity, also 46 benefiting of the inherent advantages of the electrochemical de-47 tection in terms of sensitivity, selectivity, simplicity and low 48 cost 15 . In most cases highly acidic media are needed for such 49 NPs detection, either to facilitate dissolution 16 or as source of 50 hydrogen ions for further detection based on hydrogen evolu-51 tion reaction (HER) [17][18][19][20][21][22][23] . However, the use of acid solutions is 52 not desirable for both safety reasons and the time needed for the 53 analysis, also involving additional steps after the immunoassay. 54Consequently, there is a need of NP tags that may be detected 55 in the same medium where immunoreactions take place. In this 56 context, the water oxidation reaction (WOR) occurring at neu-57 tral pH and easily catalysed by some ...

Electrochemical Biosensors Based on Nanomaterials for Early Detection of Alzheimer’s Disease

“…AuNPs have also been used as labels for AD peptide biomarkers sensing [ 105 , 106 , 107 , 108 , 109 , 110 , 111 ]. Yoo et al [ 106 ] designed a sandwich-type immunosensor for the detection of Aβ peptide by using an antibody-modified interdigitated microelectrode and AuNPs conjugated with antibodies as labels for signal amplification ( Figure 7 A).…”

“…In biosensing field, magnetic particles have become interesting tools especially as platforms for the immobilization of biological recognition elements, as their magnetic behavior allows the analyte pre-concentration and separation from complex samples, minimizing matrix effects. Taking advantage of magnetic bead platforms, Iglesias-Mayor et al [ 107 ] proposed an immunosensor for the detection of unfolded p53 peptide using bifunctional core@shell Au@Pt/Au NPs as labels ( Figure 7 B). Au@Pt/Au NPs were synthesized by Pt deposition on AuNPs surface and the subsequent galvanic replacement reaction for the substitution of some of the Pt atoms by Au.…”

“…AuPd alloys were bio-conjugated with secondary antibodies and used as labels for catalyzing the reduction of H 2 O 2 as electrochemical signal, although they achieved a LOD of only 0.45 pM. Even though the LOD may be improved, the use of AuPd alloys as catalytical labels favors its use directly in the same media as immunoreaction takes place, as it has been highlighted in above mentioned works [ 107 ], what reduces the analysis time.…”

“…At the right, the analytical signal recorded for solutions without protein (blank), containing human IgG (negative control) and containing p53 peptide (positive); and the calibration curve for p53 concentrations between 50 nM to 1000 nM (bottom). Adapted with permission from [ 107 ]. Copyright (2020) American Chemical Society.…”

Doubly-Charged Negative Ions as Novel Tunable Catalysts: Graphene and Fullerene Molecules Versus Atomic Metals

“…In recent years, research on water oxidation catalyzed by various systems, processes and mechanisms has intensified [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. The advent of the COVID-19 pandemic has also accelerated a vigorous search for and synthesis of atomic nanoparticles and catalysts for various applications (see for examples [ 17 , 18 ]). The stability of organic solar cells that is required before their actual commercialization is of particular interest here [ 19 ].…”