Robust and High Spatial Resolution Light Addressable Electrochemistry Using Hematite (α-Fe₂O₃) Photoanodes

Abstract

Light addressable/activated electrochemistry (LAE) has recently attracted attention as it can provide spatially resolved electrochemical information without using pre-patterned electrodes whose sizes and positions are unchangeable. Here, we propose hematite (α-FeO) as the photoanode for LAE, which does not require any sort of surface modification for protection or facilitating charge transfer. As experimentally confirmed with various redox species, hematite is stable enough to be used for repetitive electroanalytical measurements. More importantly, it offers exceptionally high spatial resolution so that the "virtual electrode" is exactly as large as the light spot owing to the short diffusion length of the minority carriers. Quantitative analysis of dopamine in this study shows that the hematite-based photoanode is a promising platform for many potential LAE applications including spatially selective detection of oxidizable biomolecules.

Photoelectrochemical Sensing of Hydrogen Peroxide on Hematite

“…The system is robust and we were able to experimentally detect H 2 O 2 at concentration as low as 200 nM at a physiological pH with a linear photoresponse up to 50 μM. Although more research is still needed to improve this system (i. e. optimization of the layer, study of the effect of a large panel of oxidizable molecules), it is promising, first because H 2 O 2 is of great interest in medicinal, environmental and industrial applications, and, second, because hematite is cheap and a good candidate for spatially‐resolved PEC sensing …”

“…Although more research is still needed to improve this system (i. e. optimization of the layer, study of the effect of a large panel of oxidizable molecules), it is promising, first because H 2 O 2 is of great interest in medicinal, environmental and industrial applications, and, second, because hematite is cheap and a good candidate for spatially-resolved PEC sensing. [15,17] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57…”

“…[12,13] PEC sensing decouples excitation (light) and detection (electrochemical) signals, which is expected to significantly increase the signal-tonoise ratio with respect to electrochemical sensing. [13] Besides, it is also promising because it enables 2D reaction confinement on the transducer surface (i. e. on the photoelectrode) [14,15] which can be useful for electrode reuse [16,17] or for the design of multiplexed arrays. [18,19] So far, PEC sensing has been mainly employed for the detection of biological macromolecules, [20] in immuno- [21] or apta- [22] assays and has also been explored for the detection of small organic molecules such as antioxidants [23] or glucose.…”

“…This is a severe drawback for energy-related applications [41,42] but can be a great advantage for the design of PEC sensor arrays activated by micrometer-sized spots of light. [15,17] Hematite photoanodes have been previously employed for the PEC sensing of biological macromolecules, [43,44] neurotransmitters, [17] endocrine disruptors, [45,46] glucose, [25,44] inorganic pollutants, [47] and metal cations. [48] In this paper, we report the preparation of hematite photoanodes by a convenient spin-coating/annealing method and the use of these surfaces for H 2 O 2 PEC sensing.Our hematite precursor is poly(vinylferrocene) (pvf), a Fecontaining polymer, dissolved in tetrahydrofuran (THF), which was spin-coated onto FTO slides and subsequently annealed, as shown in Figure 1a.…”

Light-addressable Electrodes for Dynamic and Flexible Addressing of Biological Systems and Electrochemical Reactions

“…Additionally, Ni-Mo (130 mM Ni(SO 3 NH 2 ), 50 mM H 3 BO 3 , and 2 mM NaMoO 4 with pH adjusted to pH 4.0) was patterned at potentials of −0.9 V for 10 s followed by a 5 s open circuit potential (+ 0.35 V) to replenish the precursor ions [105]. Similiar to amorphous silicon, also hematite (α-Fe 2 O 3 ) fullfills the requirements for a high spatial resolution through a hole diffusion length of 1-2 nm [106]. Co-Pi was deposited on hematite in different studies [106][107][108].…”