Chemistry Reference
In-Depth Information
Table 4.1 Recent approaches to metal ion sensing
Sensing mechanism
References
Fluorescent chemosensors
[
41
-
52
]
DNA-based detection
[
53
60
]
-
Paper-based electrochemical sensors
[
61
]
Silica nanotube-based sensors
[
62
]
Optical cage sensors
[
63
,
64
]
Optical nanosensors
[
65
]
Crystalline colloidal arrays
[
5
,
66
]
Plasmonic resonance energy transfer-based nanospectroscopy
[
67
]
Quantum-dot-labeled DNAzymes
[
68
]
Polydiacetylene-liposome microarrays
[
69
]
Catalytic nanomotors
[
70
]
Click chemistry-based detection
[
71
]
Graphene-based sensors
[
72
74
]
-
4.3 Conclusions
Metal cation sensors have a wide array of applications from in vitro diagnostics,
assessing the quality of water to intracellular sensing [
27
32
]. Advanced techniques
for quantifying concentrations of metal cations are based on high resolution
inductively coupled plasma mass spectrometry and atomic absorption or emission
spectroscopy [
33
-
cant
instrumentation and are non-portable. In contrast, the holographic sensors
demonstrated in this chapter offers miniaturisation, however, it does not overcome
the problem of equipment requirement since the readouts are taken by spectro-
photometers. Other methods involve quantifying the concentration of metal cations
using
35
]. However, these techniques are high cost, require signi
-
uorescence [
36
,
37
]. Such techniques do not require high-temperature
atomisation sources, but require sample preparation involving organic solvents to
allow binding of complexation agents to cations. Holographic metal ion sensors
overcome this limitation since they do not require complex sample preparation
steps. Practical solutions involve ion-selective electrodes (ISEs) that can provide
high selectivity and sensitivity for the detection metal ions such as Na
+
,K
+
,Pb
2+
and Cd
2+
[
38
,
39
], while being amenable to miniaturisation in battery-operated
devices. Although electrochemical sensors require reference solutions and custom
readout equipment to calibrate the electrodes, holographic sensors do not require
calibration. The need for improving the performance has motivated the investiga-
tion of numerous other approaches (Table
4.1
). These studies have achieved
quanti
fl
cation of metal cations at trace concentrations. However, the attributes of
being colorimetric, label/equipment-free, low-cost, lightweight, reusable or
disposable in a single metal cation sensor; while also being amenable to mass
