biosensors for endotoxin determination are listed, but since EU (endotoxin unit) is a
measurement for pyrogenic activity, comparability of different sensor methods is
restricted. In all conscience of the announced information by the authors, endotoxin
detection limits and ranges are summarized.
Therapeutic drug monitoring (TDM) aims at determining drug concentrations in
blood or blood-related samples. Many drugs can be classified as small organic
molecules. For the field of affinity-based detection in general, antibodies are the
most important strategy. However, the need of immunogenicity usually limits the
application of antibodies for small molecule detection [62]. Additionally, antibodies’
high molecular mass might reduce its feasibility in many sensor designs with regard
to low mass targets. Alternatives such as GC-MS or HPLC require highly trained
personnel [63]. Thus, aptamers are considered as an opportunity for drug monitoring
and testing.
Medication is sought to be improved by TDM for drugs demanding narrow
concentration ranges. Since many drugs are small molecules, the sensors need to
be sufficiently sensitive on a small scale. For instance, Roushani and Shahdost-fard
presented a sensor for the determination of ibuprofen [64], as the long-term medication risk of ibuprofen with regard to heart attacks is especially striking. Common
approaches for its detection are GC-MS or HPLC reaching a LoD of 1 – 8 μM
[65, 66]. Roushani and Shahdost-fard reported an ibuprofen detection down to
16 pM with a wide linear range of 50 pM up to 20 μM with high recovery rates in
spiked blood. This approach is based on functionalized Quantum dots on an electrode surface. The Quantum dots are supposed to increase the surface and therefore
the sensitivity for small molecule determination. The authors immobilized a capture
DNA probe on the Quantum dots. The aptamer contains a single-stranded target
binding site, while the rest is hybridized on the capture probe for immobilization
purposes (see Fig. 7). By a conformational change due to complex formation, an
increase of impedance was measured.
2.4 Conclusions
Aptamer-based impedimetric biosensors have been applied to a versatile range of
targets underlying the universal qualification as biotechnological tool while the
numbers of faradaic EIS applications dominate the non-faradaic ones. From cells
to small molecules, the targets of interest generally seem unlimited. Nonetheless,
aptamers for further medically relevant targets are required in order to cover the
variety of biomarker diagnostics. As a possible alternative to standard techniques,
impedimetric aptasensors have been proven to be an easy and rapid diagnostic tool
even without elaborate sample preparation due to the label-free application. In many
reports, low sample volumes of 5–100 μl were sufficient. A range of authors reported
on picomolar detection levels for small molecule and protein targets, while some
even reported (sub-)femtomolar LoD levels. Thereby, the success of aptamers as a
sensitive recognition element might root in high immobilization densities (approx.
60
J.-A. Preuß et al.
measurement for pyrogenic activity, comparability of different sensor methods is
restricted. In all conscience of the announced information by the authors, endotoxin
detection limits and ranges are summarized.
Therapeutic drug monitoring (TDM) aims at determining drug concentrations in
blood or blood-related samples. Many drugs can be classified as small organic
molecules. For the field of affinity-based detection in general, antibodies are the
most important strategy. However, the need of immunogenicity usually limits the
application of antibodies for small molecule detection [62]. Additionally, antibodies’
high molecular mass might reduce its feasibility in many sensor designs with regard
to low mass targets. Alternatives such as GC-MS or HPLC require highly trained
personnel [63]. Thus, aptamers are considered as an opportunity for drug monitoring
and testing.
Medication is sought to be improved by TDM for drugs demanding narrow
concentration ranges. Since many drugs are small molecules, the sensors need to
be sufficiently sensitive on a small scale. For instance, Roushani and Shahdost-fard
presented a sensor for the determination of ibuprofen [64], as the long-term medication risk of ibuprofen with regard to heart attacks is especially striking. Common
approaches for its detection are GC-MS or HPLC reaching a LoD of 1 – 8 μM
[65, 66]. Roushani and Shahdost-fard reported an ibuprofen detection down to
16 pM with a wide linear range of 50 pM up to 20 μM with high recovery rates in
spiked blood. This approach is based on functionalized Quantum dots on an electrode surface. The Quantum dots are supposed to increase the surface and therefore
the sensitivity for small molecule determination. The authors immobilized a capture
DNA probe on the Quantum dots. The aptamer contains a single-stranded target
binding site, while the rest is hybridized on the capture probe for immobilization
purposes (see Fig. 7). By a conformational change due to complex formation, an
increase of impedance was measured.
2.4 Conclusions
Aptamer-based impedimetric biosensors have been applied to a versatile range of
targets underlying the universal qualification as biotechnological tool while the
numbers of faradaic EIS applications dominate the non-faradaic ones. From cells
to small molecules, the targets of interest generally seem unlimited. Nonetheless,
aptamers for further medically relevant targets are required in order to cover the
variety of biomarker diagnostics. As a possible alternative to standard techniques,
impedimetric aptasensors have been proven to be an easy and rapid diagnostic tool
even without elaborate sample preparation due to the label-free application. In many
reports, low sample volumes of 5–100 μl were sufficient. A range of authors reported
on picomolar detection levels for small molecule and protein targets, while some
even reported (sub-)femtomolar LoD levels. Thereby, the success of aptamers as a
sensitive recognition element might root in high immobilization densities (approx.
60
J.-A. Preuß et al.