1 3
Topics in Current Chemistry (2020) 378:12
cells using a specific aptamer and the SAM of AuNPs. Lima et al. [224] have
recently prepared the first electrochemical immunosensor to detect dehydroepiandrosterone sulfate (DHEAS) by electrochemical impedance spectroscopy (EIS), in
order to provide an alternative method for the early diagnosis of pediatric adrenocortical carcinoma (pACC). The fabrication of this immunosensor consisted in the
modification of an oxidized glassy carbon electrode (GCE) with arginine-functionalized AuNPs (AuNPs-ARG) and anti-DHEA IgM antibodies (ox-GCE/AuNPs-ARG/
IgM). The AuNP-based immunosensor showed good sensitivity, accuracy, stability, selectivity, and feasibility to detect DHEAS with a linear range from 10.0 to
110.0 µg dL
−1
, with a LOD of 7.4 µg dL
−1
.
6.2 Electrochemical Applications of Bioconjugates Based on AgNPs
AgNPs are also important nanomaterials in electroanalysis due to their physicochemical properties. Many efforts have been made to improve the analytical methods that allow quantification of different biomarkers, metabolites and infectious
agents based on AgNPs or nanocomposites [225].
Abbaspour and co-workers described a highly selective sandwich immunosensor based on a dual-aptamer for the detection of Staphylococcus aureus [226]. In
this latter study, the authors first immobilized a biotinylated anti-S. aureus aptamer
on streptavidin-coated magnetic beads via biotin-streptavidin affinity reaction (see
section Iron oxide NPs and Fig. 7). Subsequently, the AgNPs conjugated with antiS. aureus aptamer (Apt-AgNP) were incorporated, thus completing the sandwich
design. Here, the AgNPs were assembled to the aptamer through their thiol groups
(see section Gold and silver nanoparticles and Fig. 5). The biosensor presented high
sensitivity and an extended dynamic range from 10 to 1 × 10
6
CFU/mL with a low
detection limit of 1.0 CFU/mL (S/N = 3). AgNPs are also useful for the detection
of pharmaceutical drugs. In this regard, AgNPs play an important role as electrode
modifiers due to their ability to increase the conductivity in the biosensor [225].
Ashrafi et al. [227] developed a novel, unique and sensitive biosensor to determine benzodiazepines, i.e., alprazolam, chlordiazepoxide, diazepam, oxazepam, and
clonazepam. To prepare the biosensor, the authors synthesized a nano-ink based on
AgNPs plus N-doped graphene quantum dots (Ag/N-GQD) and then electrodeposited it at the surface of a gold electrode modified with chitosan (CS), using LBL
strategy. The obtained CS-Ag/N-GQD film combined the advantages of CS, and
Ag/N-GQD with excellent electrical conductivity, biocompatibility and abundant
active sites for the electro-oxidation of the species of interest within standard and
plasma samples.
Another fine example has been reported by Roushani and Shahdost-fard [228].
These authors developed a selective electrochemical aptasensor for the ultrasensitive detection of cocaine. The aptasensor was constructed by the covalent immobilization of aptamer-functionalized AgNPs as biorecognition element, on top of
a nanocomposite made of MWCNTs, an ionic liquid (IL) and CS (MWCNTs/IL/
CS). Riboflavin was used as the redox probe in the electrochemical aptasensor for
the diagnosis of the target. The biosensor showed high sensitivity, specificity, and
115
Reprinted from the journal
Topics in Current Chemistry (2020) 378:12
cells using a specific aptamer and the SAM of AuNPs. Lima et al. [224] have
recently prepared the first electrochemical immunosensor to detect dehydroepiandrosterone sulfate (DHEAS) by electrochemical impedance spectroscopy (EIS), in
order to provide an alternative method for the early diagnosis of pediatric adrenocortical carcinoma (pACC). The fabrication of this immunosensor consisted in the
modification of an oxidized glassy carbon electrode (GCE) with arginine-functionalized AuNPs (AuNPs-ARG) and anti-DHEA IgM antibodies (ox-GCE/AuNPs-ARG/
IgM). The AuNP-based immunosensor showed good sensitivity, accuracy, stability, selectivity, and feasibility to detect DHEAS with a linear range from 10.0 to
110.0 µg dL
−1
, with a LOD of 7.4 µg dL
−1
.
6.2 Electrochemical Applications of Bioconjugates Based on AgNPs
AgNPs are also important nanomaterials in electroanalysis due to their physicochemical properties. Many efforts have been made to improve the analytical methods that allow quantification of different biomarkers, metabolites and infectious
agents based on AgNPs or nanocomposites [225].
Abbaspour and co-workers described a highly selective sandwich immunosensor based on a dual-aptamer for the detection of Staphylococcus aureus [226]. In
this latter study, the authors first immobilized a biotinylated anti-S. aureus aptamer
on streptavidin-coated magnetic beads via biotin-streptavidin affinity reaction (see
section Iron oxide NPs and Fig. 7). Subsequently, the AgNPs conjugated with antiS. aureus aptamer (Apt-AgNP) were incorporated, thus completing the sandwich
design. Here, the AgNPs were assembled to the aptamer through their thiol groups
(see section Gold and silver nanoparticles and Fig. 5). The biosensor presented high
sensitivity and an extended dynamic range from 10 to 1 × 10
6
CFU/mL with a low
detection limit of 1.0 CFU/mL (S/N = 3). AgNPs are also useful for the detection
of pharmaceutical drugs. In this regard, AgNPs play an important role as electrode
modifiers due to their ability to increase the conductivity in the biosensor [225].
Ashrafi et al. [227] developed a novel, unique and sensitive biosensor to determine benzodiazepines, i.e., alprazolam, chlordiazepoxide, diazepam, oxazepam, and
clonazepam. To prepare the biosensor, the authors synthesized a nano-ink based on
AgNPs plus N-doped graphene quantum dots (Ag/N-GQD) and then electrodeposited it at the surface of a gold electrode modified with chitosan (CS), using LBL
strategy. The obtained CS-Ag/N-GQD film combined the advantages of CS, and
Ag/N-GQD with excellent electrical conductivity, biocompatibility and abundant
active sites for the electro-oxidation of the species of interest within standard and
plasma samples.
Another fine example has been reported by Roushani and Shahdost-fard [228].
These authors developed a selective electrochemical aptasensor for the ultrasensitive detection of cocaine. The aptasensor was constructed by the covalent immobilization of aptamer-functionalized AgNPs as biorecognition element, on top of
a nanocomposite made of MWCNTs, an ionic liquid (IL) and CS (MWCNTs/IL/
CS). Riboflavin was used as the redox probe in the electrochemical aptasensor for
the diagnosis of the target. The biosensor showed high sensitivity, specificity, and
115
Reprinted from the journal