This
paper introduces a novel bacterial identification assay based on thermal
wave analysis through surface-imprinted polymers (SIPs). Aluminum
chips are coated with SIPs, serving as synthetic cell receptors that
have been combined previously with the heat-transfer method (HTM)
for the selective detection of bacteria. In this work, the concept
of bacterial identification is extended toward the detection of nine
different bacterial species. In addition, a novel sensing approach,
thermal wave transport analysis (TWTA), is introduced, which analyzes
the propagation of a thermal wave through a functional interface.
The results presented here demonstrate that bacterial rebinding to
the SIP layer resulted in a measurable phase shift in the propagated
wave, which is most pronounced at a frequency of 0.03 Hz. In this
way, the sensor is able to selectively distinguish between the different
bacterial species used in this study. Furthermore, a dose–response
curve was constructed to determine a limit of detection of 1 ×
104 CFU mL–1, indicating that TWTA is
advantageous over HTM in terms of sensitivity and response time. Additionally,
the limit of selectivity of the sensor was tested in a mixed bacterial
solution, containing the target species in the presence of a 99-fold
excess of competitor species. Finally, a first application for the
sensor in terms of infection diagnosis is presented, revealing that
the platform is able to detect bacteria in clinically relevant concentrations
as low as 3 × 104 CFU mL–1 in spiked
urine samples.
Molecularly imprinted
polymers (MIPs), synthetic polymeric receptors,
have been combined successfully with thermal transducers for the detection
of small molecules in recent years. However, up until now they have
been combined with planar electrodes which limits their use for in
vivo applications. In this work, a new biosensor platform is developed
by roll-coating MIP particles onto thermocouples, functionalized with
polylactic acid (PLLA). As a first proof-of-principle, MIPs for the
neurotransmitter dopamine were incorporated into PLLA-coated thermocouples.
The response of the synthetic receptor layer to an increasing concentration
of dopamine in buffer was analyzed using a homemade heat-transfer
setup. Binding of the template to the MIP layer blocks the heat transport
through the thermocouple, leading to less heat loss to the environment
and an overall higher temperature in the measuring chamber. The measured
temperature increase is correlated to the neurotransmitter concentration,
which enables measurement of dopamine levels in the micromolar regime.
To demonstrate the general applicability of the proposed biosensor
platform, thermocouples were functionalized with similar MIPs for
cortisol and serotonin, indicating a similar response and limit-of-detection.
As the platform does not require planar electrodes, it can easily
be integrated in, e.g., a catheter. In this way, it is an excellent
fit for the current niche in the market of therapeutics and diagnostics.
Moreover, the use of a biocompatible and disposable PLLA-layer further
illustrates its potential for in vivo diagnostics.
In this work we present the first steps towards a molecularly imprinted polymer (MIP)-based biomimetic sensor array for the detection of small organic molecules via the heat-transfer method (HTM). HTM relies on the change in thermal resistance upon binding of the target molecule to the MIP-type receptor. A flow-through sensor cell was developed, which is segmented into four quadrants with a volume of 2.5 μL each, allowing four measurements to be done simultaneously on a single substrate. Verification measurements were conducted, in which all quadrants received a uniform treatment and all four channels exhibited a similar response. Subsequently, measurements were performed in quadrants, which were functionalized with different MIP particles. Each of these quadrants was exposed to the same buffer solution, spiked with different molecules, according to the MIP under analysis. With the flow cell design we could discriminate between similar small organic molecules and observed no significant cross-selectivity. Therefore, the MIP array sensor platform with HTM as a readout technique, has the potential to become a low-cost analysis tool for bioanalytical applications.
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