Chemistry Reference
In-Depth Information
devices. Although signi
cant time has been devoted to spectrophotometric read-
outs, the attribute of being equipment-free should not be overlooked. The use of
external readers is a barrier for the existing assays, yet this will be a greater
challenge in adopting holographic diagnostics. In addition to the app described in
this thesis, there are newer apps that might compensate for the lighting conditions
[
50
] and location identi
cation of multiple colorimetric sensors [
51
]. Direct com-
petition of the app developed in this thesis is handheld readers. Commercial readers
such as RDS-1500 Pro (Detekt Biomedical, Austin, TX), Defender TSR
™
R-5001
(Alexeter Technologies LLC, Wheeling, IL), LFDR101 (Forsite Diagnostics Ltd,
York, U.K.) and UNISCAN
™
Immunoassay Rapid Test Reader (Unison Biotech,
Taiwan) can read colorimetric and
fl
fluorescent assays. Currently, LRE and Wiagen
readers lead the market in
fidelity and sensitivity. These semi-quantitative lateral-
fl
flow assay readers offer adequate sensitivity, but are high cost ($1
$2 k). All the
-
readout devices outlined are test-strip speci
c, in other words not standard reading
platforms. The smartphone application described in this thesis has the potential to
contribute to the development of universal and connected readout devices.
7.5 The Vision for Holographic Sensors
Sensing mechanisms for point-of-care tests are primarily based on gold colloids
with antibody/antigen interactions, molecular-dye-based sensors and electrochem-
istry [
52
]. These formats are ubiquitous and universally applicable for the use of
simple, qualitative and low-cost point-of-care applications, while also having
enough capability to be utilised in sensitive, quantitative and multiplex assays.
Therefore, academic efforts should focus on holographic sensing applications that
are not currently feasible with the existing sensing platforms and explore areas in
great need. These niche areas are reusable, implantable, wearable, wireless and
powerless devices, possibly targeting analytes at
/mM concentrations. The ulti-
mate challenge will be to justify the performance and the cost to attain a potential
“
µ
application, which was achieved through urine dipstick of molecular-dye-
based sensing, pregnancy test of NP-based assays, and blood glucose monitoring of
electrochemical sensing. Other commercialisation routes may require the devel-
opers to embrace the holographic sensors as an enabling platform, which might be
an integral part of another sensing technology. The holographic sensors offer
unique attributes since they not only provide the interrogation and reporting
transducer, but they also have the analyte-responsive hydrogel, rendering them
label-free and reusable with remote sensing capability [
53
]. The single-pulse laser
patterning represents the
killer
”
first step towards producing multiplex hydrogel-based
holographic sensors that can display 3D images. The future of holographic sensing
is at the interface of photopolymerisation, printing, digital holography and inte-
gration with micro
fl
uidic devices,
implantable chips and contact
lenses. It
is
envisioned that holographic sensors will
find applications from in vitro diagnostics
to dynamic displays to security devices (Fig.
7.3
).
