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Solving Analytical Challenges with Thin Layer Electrochemistry
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0001-7941-2312
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The decentralization of chemical sensing to attain environmental-related information is today highly desirable to increase the knowledge on biological or geological events as well as effluents. The current state of the field moves toward submersible probes; chemical sensors implemented into submersible devices for quantifying analytes over extended times. However, many sensors are still not robust enough for such applications. Additionally, the detections of most analytes require reagent addition and other steps before analysis (i.e., pre-treatments). For such analyses to be implemented in decentralized measurements, it would be beneficial to find reagentless approaches to modify samples and avoid waste associated with the reagent addition. This thesis aimed to develop such strategies using different solid materials capable of imposing ion-transfer events (actuators) under electrochemical control, to achieve measuring the analytes in the same sample using chemical sensors. Both actuators and sensors were jointly employed in thin layer (or near thin layer) samples, inside newly designed 3D-printed cells. This allowed for small sample volumes (ca 100 µm thicknesses) down to 0.5 µL to be analyzed, and resulted in fast, non-diffusion limited measurements that facilitated the sensor-actuator concepts. 

First, acidification of thin layer samples using polyaniline (PANI) was investigated. By electrochemical oxidation of PANI, its molecular structure changed resulting in hydrogen ions (acid) being delivered to the thin layer sample within two minutes or less, shifting its pH from ca 8 down to 2–3. By combining PANI and pH-sensors, reliable detection of alkalinity in real and artificial water samples could be achieved for a period of two weeks and possibly more. Also, by combining the PANI-based acidification with planar optodes capable of measuring pH or CO2 with high spatial resolution, buffer capacity or dissolved inorganic carbon (DIC) gradients could be resolved in a 2D domain with sub-mm resolution. PANI-based acidification was tested for sensing several environmental samples, including freshwater plants, brackish water, seawater, and soil, presenting great versatility in analytical performance. 

Second, a concept of selective deionization of thin layer samples was developed. The importance of such a concept is related to the selectivity of ion-based measurements, where ions such as Li+ or NH4+ are difficult to detect in real samples because of interfering ions increasing their limit of detection (LOD). Non-faradic processes were explored to remove such interferents by using carbon nanotubes (CNTs) for modulating the ion transfer with the sample. To facilitate selective deionization to only remove one ion species, the CNTs were covered with ultra-thin ion-selective membranes (ISMs; ca 200 nm thick). The tandem of CNTs-ISM was found to be capable of selectively removing multiple different cations, proven with the monitoring from both potentiometric sensors and optodes additionally implemented into the thin layer sample. Overall, the CNTs-ISM tandem shows great promise for lowering the LOD of chemical sensors in complex matrixes such as biological or environmental samples, which could aid to decentralized measurements in the future.

Abstract [sv]

Införandet av kemiska sensorer för decentraliserade mätningar utanför laboratoriemiljö är idag eftersträvat för att öka kunskaperna kring människans påverkan på naturen, samt för att öka förståelsen kring biologiska och geologiska händelseförlopp i naturen. Idag riktas mycket fokus inom den analytiska kemin på att utveckla kemiska sensorer som kan kopplas på nedsänkbara sonder och direkt mäta halter av ämnen i naturliga vatten över en längre tid. De flesta kemiska sensorer som har utvecklats idag är dessvärre inte robusta nog för längre mätningar, och vissa ämnen kan inte mätas utan reagens tillförs provet. En lösning till denna utmaning skulle vara att finna reagenslösa lösningar för att justera provernas sammansättning inför analys. Denna avhandling hade som mål att utveckla sådana metodologier baserade på material vilka kan styra jontransporter under elektrokemisk kontroll (aktuatorer), samtidigt som deras förmåga att modulera dessa har kvantifierats med kemiska sensorer. Både aktuatorer och sensorer implementerades i tunnskiktsprover i 3D-printade celler. Detta medförde att mycket små volymer av prover (ca 100 µm tunna prover) ned till ca 0.5 µL kunde analyseras, vilket resulterade i snabba mätningar som inte var begränsade av diffusionen.

Först undersöktes materialet polyanilin (PANI) för att justera pH i tunnskiktsprover. När den elektrokemiska potentialen skiftar för PANI så ändras dess molekylära struktur, vilket leder till att vätejoner (syre) bindningar släps från materialet till tunnskiktsprovet, vilket sänker dess pH från ca 8 ner till 2-3. I kombination med en pH-elektrod i tunnskiktsprover kunde tillförlitliga alkalinitet-mätningar utföras i riktiga och artificiella prover över en period av två veckor, och möjligen ännu längre. Genom att kombinera PANI-försurningen med plana optoder som kunde mäta pH och CO2 med hög bildupplösning kunde koncentrationer av buffertkapacitet och totalt oorganiskt kol (DIC) mätas i 2D med en hög upplösning (mm>). Den PANI-baserade försurningen testades i diverse prover; på färskvatten växter, i bräckt vatten, havsvatten och i jordprover, vilket påvisar dess exceptionellt mångsidiga analytiska prestation.

Därefter utvecklades konceptet för selektiv avjonisering av tunnskiktsprover. Detta koncept är extra intressant när den ställs i kontexten att vissa jonmätningar inte kan utföras på grund utav att de störs ut av interferenser i provet vilket höjer deras detektionsgränser (LOD), vilket är fallet för Li+ och NH4+-sensorer. Icke-Faradiska processer utforskades baserade på kolnanorör (CNTs) för att modulera jonöverföringar. För att uppnå selektivitet för att avlägsna enbart en jonart så täcktes CNTs med ultra-tunna jonselektiva membran (ISMs; ca 200 nm). Resultaten påvisade att det är möjligt att selektivt avjonisera prov genom denna CNT-ISM tandem, och flera olika joner påvisades möjliga att undergå denna process med hjälp av potentiometriska sensorer och optoder implementerade i den 3D-printade tunnskiktscellen. Överlag visar denna CNTs-ISM tandem potential för att kunna sänka LODs för sensorer i komplexa matriser, såsom biologiska och miljöprover, vilket skulle kunna bidra till decentraliserade mätningar i framtiden.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2023. , p. 84
Series
TRITA-CBH-FOU ; 2023:35
Keywords [en]
Thin Layer Electrochemistry, Polyaniline, Carbon nanotubes, Ion-selective electrodes, Ionophores, Electrochemical Sensors, Alkalinity, Deionization, Chemical Imaging
Keywords [sv]
Tunnskiktselektrokemi, polyanilin, kolnanorör, jonselektiva elektroder, jonoforer, elektrokemiska sensorer, Alkalinitet, avjonisering, chemical imaging
National Category
Analytical Chemistry Materials Chemistry Physical Chemistry
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-335376ISBN: 978-91-8040-666-6 (print)OAI: oai:DiVA.org:kth-335376DiVA, id: diva2:1794504
Public defence
2023-10-06, F3, Lindstedsvägen 26, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 2023-09-06

Available from: 2023-09-06 Created: 2023-09-05 Last updated: 2023-09-26Bibliographically approved
List of papers
1. Polyaniline Films as Electrochemical-Proton Pump for Acidification of Thin Layer Samples
Open this publication in new window or tab >>Polyaniline Films as Electrochemical-Proton Pump for Acidification of Thin Layer Samples
2019 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 91, no 23, p. 14951-14959Article in journal (Refereed) Published
Abstract [en]

Here, we provide the first experimental evidence of proton release from polyaniline (PANI) films subjected to anodic potentials at environmental pHs. We conducted an extensive characterization of unpolarized/polarized PANI films—synthesized by traditional sequential voltammetric scanning—by using spectroelectrochemistry, synchrotron radiation-X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure, and potentiometric pH sensing in the vicinity of the PANI layer. This new insight enables the utilization of PANI as a proton pump, which is actively tuned through an electrochemical pulse, so as to controllably acidify well-confined thin layer samples. Furthermore, we demonstrate the analytical significance of this system by measuring the alkalinity of artificial and natural water samples by using two faced planar PANI electrodes, one working as a proton source and the other one as pH electrode. Finally, the impact of this approach is 2-fold: (i) all-solid-state electrode materials may be used with devisible consequences in miniaturized and implementable submersible probes, and (ii) rapid determination of alkalinity as compared to traditional approaches together with a versatility in pH adjustment in any kind of sample, among other applications.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Analytical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-335368 (URN)10.1021/acs.analchem.9b03402 (DOI)000500838600027 ()31691565 (PubMedID)2-s2.0-85075424423 (Scopus ID)
Funder
Swedish Research Council, VR-2017-4887KTH Royal Institute of Technology, K-2017-0371
Note

QC 20230905

Available from: 2023-09-05 Created: 2023-09-05 Last updated: 2023-10-09Bibliographically approved
2. Reagentless Acid–Base Titration for Alkalinity Detection in Seawater
Open this publication in new window or tab >>Reagentless Acid–Base Titration for Alkalinity Detection in Seawater
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2021 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 93, no 42, p. 14130-14137Article in journal (Refereed) Published
Abstract [en]

Herein, we report on a reagentless electroanalytical methodology for automatized acid–base titrations of water samples that are confined into very thin spatial domains. The concept is based on the recent discovery from our group (Wiorek, A. Anal. Chem. 2019, 91, 14951−14959), in which polyaniline (PANI) films were found to be an excellent material to release a massive charge of protons in a short time, achieving hence the efficient (and controlled) acidification of a sample. We now demonstrate and validate the analytical usefulness of this approach with samples collected from the Baltic Sea: the titration protocol indeed acts as an alkalinity sensor via the calculation of the proton charge needed to reach pH 4.0 in the sample, as per the formal definition of the alkalinity parameter. In essence, the alkalinity sensor is based on the linear relationship found between the released charge from the PANI film and the bicarbonate concentration in the sample (i.e., the way to express alkalinity measurements). The observed alkalinity in the samples presented a good agreement with the values obtained by manual (classical) acid–base titrations (discrepancies <10%). Some crucial advantages of the new methodology are that titrations are completed in less than 1 min (end point), the PANI film can be reused at least 74 times over a 2 week period (<5% of decrease in the released charge), and the utility of the PANI film to even more decrease the final pH of the sample (pH ∼2) toward applications different from alkalinity detection. Furthermore, the acidification can be accomplished in a discrete or continuous mode depending on the application demands. The new methodology is expected to impact the future digitalization of in situ acid–base titrations to obtain high-resolution data on alkalinity in water resources.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2021
National Category
Analytical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-335369 (URN)10.1021/acs.analchem.1c02545 (DOI)000711718700015 ()34652903 (PubMedID)2-s2.0-85118280764 (Scopus ID)
Funder
Swedish Research Council, VR-2017-4887Swedish Research Council, VR-2019-04142
Note

QC 20230906

Available from: 2023-09-05 Created: 2023-09-05 Last updated: 2023-09-06Bibliographically approved
3. Imaging Sample Acidification Triggered by Electrochemically Activated Polyaniline
Open this publication in new window or tab >>Imaging Sample Acidification Triggered by Electrochemically Activated Polyaniline
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2022 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 94, no 40, p. 13647-13651Article in journal (Refereed) Published
Abstract [en]

In this letter, we demonstrate 2D acidification of samples at environmental and physiological pH with an electrochemically activated polyaniline (PANI) mesh. A novel sensor–actuator concept is conceived for such a purpose. The sample is sandwiched between the PANI (actuator) and a planar pH optode (sensor) placed at a very close distance (∼0.50 mm). Upon application of a mild potential to the mesh, in contrast to previously reported acidification approaches, PANI releases a significant number of protons, causing an acid–base titration in the sample. This process is monitored in time and space by the pH optode, providing chemical imaging of the pH decrease along the dynamic titration via photographic acquisition. Acidification of samples at varying buffer capacity has been investigated: the higher the buffer capacity, the more time (and therefore proton charge) was needed to reach a pH of 4.5 or even lower. Also, the ability to map spatial differences in buffer capacity within a sample during the acid–base titration was unprecedentedly proven. The sensor–actuator concept could be used for monitoring certain analytes in samples that specifically require acidification pretreatment. Particularly, in combination with different optodes, dynamic mapping of concentration gradients will be accessible in complex environmental samples ranging from roots and sediments to bacterial aggregates.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2022
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-335371 (URN)10.1021/acs.analchem.2c03409 (DOI)000864682000001 ()36166620 (PubMedID)2-s2.0-85139190247 (Scopus ID)
Funder
Swedish Research Council, VR-2019-04142
Note

QC 20230906

Available from: 2023-09-05 Created: 2023-09-05 Last updated: 2023-09-06Bibliographically approved
4. Imaging of CO2 and Dissolved Inorganic Carbon via Electrochemical Acidification–Optode Tandem
Open this publication in new window or tab >>Imaging of CO2 and Dissolved Inorganic Carbon via Electrochemical Acidification–Optode Tandem
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2023 (English)In: ACS Sensors, E-ISSN 2379-3694, Vol. 8, no 7, p. 2843-2851Article in journal (Refereed) Published
Abstract [en]

Dissolved inorganic carbon (DIC) is a key component of the global carbon cycle and plays a critical role in ocean acidification and proliferation of phototrophs. Its quantification at a high spatial resolution is essential for understanding various biogeochemical processes. We present an analytical method for 2D chemical imaging of DIC by combining a conventional CO2 optode with localized electrochemical acidification from a polyaniline (PANI)-coated stainless-steel mesh electrode. Initially, the optode response is governed by local concentrations of free CO2 in the sample, corresponding to the established carbonate equilibrium at the (unmodified) sample pH. Upon applying a mild potential-based polarization to the PANI mesh, protons are released into the sample, shifting the carbonate equilibrium toward CO2 conversion (>99%), which corresponds to the sample DIC. It is herein demonstrated that the CO2 optode–PANI tandem enables the mapping of free CO2 (before PANI activation) and DIC (after PANI activation) in complex samples, providing high 2D spatial resolution (approx. 400 μm). The significance of this method was proven by inspecting the carbonate chemistry of complex environmental systems, including the freshwater plant Vallisneria spiralis and lime-amended waterlogged soil. This work is expected to pave the way for new analytical strategies that combine chemical imaging with electrochemical actuators, aiming to enhance classical sensing approaches via in situ (and reagentless) sample treatment. Such tools may provide a better understanding of environmentally relevant pH-dependent analytes related to the carbon, nitrogen, and sulfur cycles.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2023
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-335372 (URN)10.1021/acssensors.3c00790 (DOI)001020630000001 ()37392165 (PubMedID)2-s2.0-85164918759 (Scopus ID)
Funder
Swedish Research Council, VR-2019-04142
Note

QC 20230905

Available from: 2023-09-05 Created: 2023-09-05 Last updated: 2024-03-05Bibliographically approved
5. Selective Ion Capturing via Carbon Nanotubes Charging
Open this publication in new window or tab >>Selective Ion Capturing via Carbon Nanotubes Charging
2022 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 94, no 21, p. 7455-7459Article in journal (Refereed) Published
Abstract [en]

We present a phenomenon consisting of the synergistic effects of a capacitive material, such as carbon nanotubes (CNTs), and an ion-selective, thin-layer membrane. CNTs can trigger a charge disbalance and propagate this effect into a thin-layer membrane domain under mildly polarization conditions. With the exceptional selectivity and the fast establishment of new concentration profiles provided by the thin-layer membrane, a selective ion capture from the solution is expected, which is necessarily linked to the charge generation on the CNTs lattice. As a proof-of-concept, we investigated an arrangement based on a layer of CNTs modified with a nanometer-sized, potassium-selective membrane to conform an actuator that is in contact with a thin-layer aqueous solution (thickness of 50 μm). The potassium ion content was fixed in the solution (0.1–10 mM range), and the system was operated for 120 s at −400 mV (with respect to the open circuit potential). A 10-fold decrease from the initial potassium concentration in the thin-layer solution was detected through either a potentiometric potassium-selective sensor or an optode confronted to the actuator system. This work is significant, because it provides empirical evidence for interconnected charge transfer processes in CNT–membrane systems (actuators) that result in controlled ion uptake from the solution, which is monitored by a sensor. One potential application of this concept is the removal of ionic interferences in a sample by means of the actuator to enhance precision of analytical assessments of a charged or neutral target in the sample with the sensor.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2022
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-335370 (URN)10.1021/acs.analchem.2c00797 (DOI)000807338400002 ()35579547 (PubMedID)2-s2.0-85131405157 (Scopus ID)
Funder
Swedish Research Council, VR-2017-4887
Note

QC 20230906

Available from: 2023-09-05 Created: 2023-09-05 Last updated: 2023-09-06Bibliographically approved
6. Selective Deionization of Thin-Layer Samples using the Tandem Carbon Nanotubes – Polymeric Membranes
Open this publication in new window or tab >>Selective Deionization of Thin-Layer Samples using the Tandem Carbon Nanotubes – Polymeric Membranes
(English)Manuscript (preprint) (Other academic)
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-335375 (URN)
Note

QC 20230906

Available from: 2023-09-05 Created: 2023-09-05 Last updated: 2023-09-06Bibliographically approved

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