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Size matters: problems and advantages associated with highly miniaturized sensors.

Dahlin AB - Sensors (Basel) (2012)

Bottom Line: Still, all issues discussed are generic in the sense that the conclusions apply to practically all types of surface sensitive techniques.Instead, it is suggested that sensing on the microscale often offers a good compromise between utilizing some possible advantages of miniaturization while avoiding the complications.This means that ensemble measurements on multiple nanoscale sensors are preferable instead of utilizing a single transducer entity.

View Article: PubMed Central - PubMed

Affiliation: Division of Bionanophotonics, Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden. adahlin@chalmers.se

ABSTRACT
There is no doubt that the recent advances in nanotechnology have made it possible to realize a great variety of new sensors with signal transduction mechanisms utilizing physical phenomena at the nanoscale. Some examples are conductivity measurements in nanowires, deflection of cantilevers and spectroscopy of plasmonic nanoparticles. The fact that these techniques are based on the special properties of nanostructural entities provides for extreme sensor miniaturization since a single structural unit often can be used as transducer. This review discusses the advantages and problems with such small sensors, with focus on biosensing applications and label-free real-time analysis of liquid samples. Many aspects of sensor design are considered, such as thermodynamic and diffusion aspects on binding kinetics as well as multiplexing and noise issues. Still, all issues discussed are generic in the sense that the conclusions apply to practically all types of surface sensitive techniques. As a counterweight to the current research trend, it is argued that in many real world applications, better performance is achieved if the active sensor is larger than that in typical nanosensors. Although there are certain specific sensing applications where nanoscale transducers are necessary, it is argued herein that this represents a relatively rare situation. Instead, it is suggested that sensing on the microscale often offers a good compromise between utilizing some possible advantages of miniaturization while avoiding the complications. This means that ensemble measurements on multiple nanoscale sensors are preferable instead of utilizing a single transducer entity.

No MeSH data available.


Suitable volumetric flow for efficient delivery of molecules to the sensor as a function of sensor size. The geometry is based on the channel in Figure 1 and the flow is calculated from Equation (5). A diffusion constant of 10−10 m2/s is assumed for the Brownian motion perpendicular to the surface. Flow rates higher than Qcapt will still increase the delivery rate of molecules but relatively little.
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f3-sensors-12-03018: Suitable volumetric flow for efficient delivery of molecules to the sensor as a function of sensor size. The geometry is based on the channel in Figure 1 and the flow is calculated from Equation (5). A diffusion constant of 10−10 m2/s is assumed for the Brownian motion perpendicular to the surface. Flow rates higher than Qcapt will still increase the delivery rate of molecules but relatively little.

Mentions: The flow rate calculated from Equation (5) represents a compromise between enhancing mass transport to the sensor while preserving decent capture efficiency, i.e., the probability that a molecule introduced with the flow actually encounters the sensor surface should be around 50%. Of course, if one has practically unlimited amounts of sample volume available, it is still possible to increase the flow (Q > Qcapt) and further enhance ∂Γ/∂t. However, the effect becomes much weaker and Γ approaches a Q1/3 dependence [8], which is also what happens for large channels [24] (h → ∞). Therefore, Equation (5) is still important because it indicates the absolute flow rate at which it becomes difficult to achieve further enhancement from flow in diffusion limited systems. Figure 3 shows results from using Equation (5) to calculate Qcapt for different A and a few different h, fixing D as 10−10 m2/s. Clearly, a small A is associated with a low Qcapt, although the flow channel height also is important. The larger sensors (up to 1 cm2) have no problems capturing molecules even at relatively high Q. In contrast, the nanosensors (A down to 10 × 10 nm) essentially cannot be used together with flow at all if good capture efficiency should be maintained, regardless of the flow channel height. Admittedly, for small sensors some enhancement is still possible even in the Q1/3 limit since Q can be increased so many orders of magnitude above Qcapt. Note that it has been assumed that the flow channel width is equal to the width of the sensor spot, which is an arbitrary rectangle. It should also be kept in mind that for binding controlled by diffusion under convection one gets an inhomogeneous Γ in the direction of the flow [24].


Size matters: problems and advantages associated with highly miniaturized sensors.

Dahlin AB - Sensors (Basel) (2012)

Suitable volumetric flow for efficient delivery of molecules to the sensor as a function of sensor size. The geometry is based on the channel in Figure 1 and the flow is calculated from Equation (5). A diffusion constant of 10−10 m2/s is assumed for the Brownian motion perpendicular to the surface. Flow rates higher than Qcapt will still increase the delivery rate of molecules but relatively little.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3376590&req=5

f3-sensors-12-03018: Suitable volumetric flow for efficient delivery of molecules to the sensor as a function of sensor size. The geometry is based on the channel in Figure 1 and the flow is calculated from Equation (5). A diffusion constant of 10−10 m2/s is assumed for the Brownian motion perpendicular to the surface. Flow rates higher than Qcapt will still increase the delivery rate of molecules but relatively little.
Mentions: The flow rate calculated from Equation (5) represents a compromise between enhancing mass transport to the sensor while preserving decent capture efficiency, i.e., the probability that a molecule introduced with the flow actually encounters the sensor surface should be around 50%. Of course, if one has practically unlimited amounts of sample volume available, it is still possible to increase the flow (Q > Qcapt) and further enhance ∂Γ/∂t. However, the effect becomes much weaker and Γ approaches a Q1/3 dependence [8], which is also what happens for large channels [24] (h → ∞). Therefore, Equation (5) is still important because it indicates the absolute flow rate at which it becomes difficult to achieve further enhancement from flow in diffusion limited systems. Figure 3 shows results from using Equation (5) to calculate Qcapt for different A and a few different h, fixing D as 10−10 m2/s. Clearly, a small A is associated with a low Qcapt, although the flow channel height also is important. The larger sensors (up to 1 cm2) have no problems capturing molecules even at relatively high Q. In contrast, the nanosensors (A down to 10 × 10 nm) essentially cannot be used together with flow at all if good capture efficiency should be maintained, regardless of the flow channel height. Admittedly, for small sensors some enhancement is still possible even in the Q1/3 limit since Q can be increased so many orders of magnitude above Qcapt. Note that it has been assumed that the flow channel width is equal to the width of the sensor spot, which is an arbitrary rectangle. It should also be kept in mind that for binding controlled by diffusion under convection one gets an inhomogeneous Γ in the direction of the flow [24].

Bottom Line: Still, all issues discussed are generic in the sense that the conclusions apply to practically all types of surface sensitive techniques.Instead, it is suggested that sensing on the microscale often offers a good compromise between utilizing some possible advantages of miniaturization while avoiding the complications.This means that ensemble measurements on multiple nanoscale sensors are preferable instead of utilizing a single transducer entity.

View Article: PubMed Central - PubMed

Affiliation: Division of Bionanophotonics, Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden. adahlin@chalmers.se

ABSTRACT
There is no doubt that the recent advances in nanotechnology have made it possible to realize a great variety of new sensors with signal transduction mechanisms utilizing physical phenomena at the nanoscale. Some examples are conductivity measurements in nanowires, deflection of cantilevers and spectroscopy of plasmonic nanoparticles. The fact that these techniques are based on the special properties of nanostructural entities provides for extreme sensor miniaturization since a single structural unit often can be used as transducer. This review discusses the advantages and problems with such small sensors, with focus on biosensing applications and label-free real-time analysis of liquid samples. Many aspects of sensor design are considered, such as thermodynamic and diffusion aspects on binding kinetics as well as multiplexing and noise issues. Still, all issues discussed are generic in the sense that the conclusions apply to practically all types of surface sensitive techniques. As a counterweight to the current research trend, it is argued that in many real world applications, better performance is achieved if the active sensor is larger than that in typical nanosensors. Although there are certain specific sensing applications where nanoscale transducers are necessary, it is argued herein that this represents a relatively rare situation. Instead, it is suggested that sensing on the microscale often offers a good compromise between utilizing some possible advantages of miniaturization while avoiding the complications. This means that ensemble measurements on multiple nanoscale sensors are preferable instead of utilizing a single transducer entity.

No MeSH data available.