Search

Advanced insights into electroanalytical systems enabled developing sensors for health-care, environment and industrial processes monitoring. Manufacturing miniaturized devices has become a peculiar research topic for lower-cost and easy- to-use analytical solutions. In scope of this, inkjet printing (IJP) has emerged as a powerful production technology ; it is digitally controlled, mask-less and non-contact, fast, low- cost, environmentally viable, and suitable for upscaling. A previously published concept of a reference membrane based on the photoreduction of AgCl in a poly(vinyl butyral) (PVB) methanol solution [1] could be further developed towards manufacturing solid-state reference electrodes (SSRE) by means of IJP. [2] We have developed and optimized two PVB-based reference membrane solutions for in situ production of Ag/AgCl-based SSRE by means of IJP. The two membranes were prepared using tertiary solutions of AgNO3 and CaCl2 in methanol, ethylene glycol and butanol, with the aid of commercially available surfactant Triton X-100. The solutions were sequentially added on top of inkjet printed planar silver and carbon electrodes. Upon mixing the solutions AgCl is formed, which is then partially reduced by intense pulsed light (IPL). We have optimized the weight percentage of PVB, the degree of photoreduction and the conditioning procedure to obtain a stable reference electrode potential. The response to chloride and other ions was evaluated via potentiometry and electrochemical impedance spectroscopy, along with the influence of pH and light. Approaches like this could enable large scale manufacturing of low-cost miniaturized solid-state reference electrodes to find use in emerging chemical sensing scenarios.

Intense Pulsed Light (IPL) is a short pulsed flash (down to 100 µs) of a xenon lamp emitting mostly visible light (190 nm to 1100 nm), which is caused by the formation of an electric arc between high- voltage tungsten electrodes (1000 V – 3000 V). Compared to other reduction methods, IPL photoreduction does not require using reducing agents ; it is energy and time-efficient, 1 thereby meeting the requirements of sustainable development. In this study, IPL photoreduction was evaluated in two different systems (Figure 1). The first system was the dispersion of graphene oxide (GO) in water, buffer (pH= 10), ethanol, and ethanol with poly(vinyl butyral) (PVB). The purpose of the experiment was to determine the influence of the dispersing agent on photoreduction and to define the optimal parameters of the IPL system that provide a highquality product. Additionally, the dispersion stability of the product was evaluated. The degree of reduction was verified by UV/Vis spectrophotometry ; the largest degree of reduction and most stable dispersion was found in the buffer (pH= 10). The second system was a methanol solution of AgCl and NaCl in the PVB polymer matrix. IPL partial photoreduction was performed at mild IPL parameters. Silver nanoparticles were formed, as evidenced by the peak at 420 nm in the UV/Vis spectra ; with the excess of AgCl and NaCl still present in the PVB matrix. The obtained polymer- inorganic salts hybrid was used as a reference membrane (RM) in a proof-of-concept experiment for the development of a planar all-solidstate reference electrode. The RM has shown a great capability of ensuring potential stability in Cl– and NO3– containing solutions, as well as in a broad pH range.

Razvoj čvrtofaznih referentnih elektroda stabilnog potencijala nužan je za integraciju u minijaturizirane potenciometrijske senzorske sustave. Ovdje su predstavljeni prvi koraci u razvoju čvrstofaznih plošnih Ag/AgCl tiskanih referentnih elektroda. Ispitane su dvije izvedbe čvrstofaznih elektroda: 1. štapićasta Ag-elektroda je kemijski klorirana primjenom željezova(III) klorida te površinski oslojena referentnom membranom na bazi poli(vinil butirala) (PVB) ; 2. formulirana je referentna Ag/AgCl pasta primjenom inovativne tehnike fotoredukcije intenzivnom pulsirajućom svjetlošću (IPL) i nanesena na štapićastu elektrodu od staklastog ugljika. Optimirani su uvjeti kemijskog kloriranja i fotoredukcije te potreban volumen PVB-membrane i referentne paste. Ispitan je odziv elektroda u vodenim otopinama KCl različitih koncentracija ; u oba slučaja ostvaren je prihvatljiv naponski odziv. Nadalje je ispitan odziv u otopinama različitih soli, uključujući NaNO3, NaCl te CaCl2 ; ispitan je utjecaj pH na elektrodni odziv te je izvršena usporedna karakterizacija komercijalne ionsko-selektivne elektrode uz pripravljene čvrstofazne referentne elektrode te konvencionalnu Ag/AgCl elektrodu s unutarnjim elektrolitom. Konačno, izvršen je transfer optimiranih referentnih membrana na inkjet otisnutu srebrnu elektrodu u svrhu demonstracije plošne referentne elektrode. Ovaj rad financirala je Hrvatska zaklada za znanost projektom UIP-2020-02-9139.

Continuous chemical monitoring presents an imperative for environmental and healthcarerelated analysis, often inaccessible to classical analytical techniques, such as HPLC and UV/Vis spectroscopy. Within the scope of this work, miniaturized planar electrochemical sensor platforms set up in an all- solid-state manner have been developed by inkjet printing. We developed, characterized and optimized the printing process of a planar all-solid-state ammonium ion-selective electrode (NH4-ASS-ISE) (Figure 1). Silver connection pads were made by inkjet printing commercial Ag-ink on flexible polymeric substrates. For the solid contacts, we have previously formulated an inkjet printable water-ethanol-ethylene glycol graphene suspension.1 The number of graphene overprints and the volume of the drop-cast ammoniumselective membrane were optimized with the aid of electrochemical impedance analysis, cyclic voltammetry and potentiometry. NH4- ASS-ISE prepared by 50 graphene ink overprints and dropcast with 120 μL of the ammonium-selective membrane demonstrated the best properties, in terms of sensitivity (64.3 mV/dec in the linear range from 10–4 M to 10–1 M NH4Cl), potential stability, reproducibility of measurements (n = 3), reversibility, and linearity (R2 = 0.9980).

Miniaturized solid-state reference electrodes (SSRE) with a stable potential are needed to enable novel application scenarios of potentiometric sensing. Inkjet printing has recently been highlighted as a prospective technology for the development of such electrodes in a high-throughput and cost-effective manner [1]. We present here the first steps in the development of inkjet-printed Ag/AgCl SSREs. Two different electrode designs were tested: First, a disk silver electrode was chemically chlorinated using iron(III) chloride and surface coated with a poly(vinyl butyral) (PVB) reference membrane [1] – RE1. Second, a reference Ag/AgCl paste was formulated based on AgCl reduction in a PVB solution [2] – RE2, which enabled development on non-silver (glassy carbon) disk electrodes. An innovative intense pulsed light (IPL) photoreduction technique was applied for AgCl reduction in the paste. The conditions of chemical chlorination and IPL photoreduction parameters were optimized, as well as the required volumes of the reference membranes and conditioning times. The electrodes were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The response of the electrodes in aqueous solutions of various salts, including KCl, NaNO3, NaCl, and CaCl2 of different concentrations was examined, as well as the electrodes’ response to pH changes. In all cases, an acceptable voltage response was achieved, and both types of electrodes were stable over a wide pH range. Further on, comparative characterization of a commercial ion-selective electrode with prepared SSREs against a conventional (internal electrolyte based) double junction Ag/AgCl electrode was performed, yielding similar sub-Nernstian slopes for all systems. Finally, the optimized reference membranes were transferred onto planar electrodes fabricated by inkjet printing of silver and graphene inks and characterized correspondingly. Acknowledgment This work was funded by the Croatian Science Foundation under grant UIP-2020-02-9139. References 1. A. Moya, R. Pol, A. Martínez-Cuadrado, R. Villa, G. Gabriel, M. Baeza, Stable Full-Inkjet- Printed Solid-State Ag/AgCl Reference Electrode, Anal. Chem. 2019, 91, 24, 15539–15546. 2. T. Guinovart Gaston, A. Crespo, F. X. Rius, F. J. Andrade, A reference electrode based on polyvinyl butyral (PVB) polymer for decentralized chemical measurements, Anal. Chim. Acta 2014, 821, 22, 72–80.

Miniaturized solid-state electrodes fabricated by inkjet printing provide innovative application scenarios of potentiometric sensing [1]. We present here the development of a reference paste that – when used on a printed electrical contact – gives a reference electrode. Such a paste was prepared by an innovative intense pulsed light (IPL) photoreduction of a 10% polyvinyl butyral (PVB) in a methanol solution of AgNO3 and NaCl, yielding a silver/silver chloride reference paste (RM). Firstly, the RM was drop cast on a glassy carbon disk electrode (RM-GC) [2]. The potentiometric response of the electrode in aqueous solutions of KCl, NaNO3, NaCl, and CaCl2 of different concentrations versus commercial reference electrode, as well as the response of the electrode to pH changes, was examined. A stable electrode potential was achieved by optimizing: IPL photoreduction parameters, volumes of the RM, and conditioning time. Lastly, the optimized reference membrane was transferred onto a planar inkjet printed silver electrode and characterized correspondingly.

Inkjet printing of metal nanoparticle-based conductive inks has recently been utilized abundantly as an attractive technology to replace traditional electronics manufacturing processes. Due to their remarkable electrical conductivity, silver nanoparticles (AgNPs) are the material of choice for printed flexible electronics, but formulating inks which are stable in different solvents, meet printer requirements, and adhere well to plastic substrates remains a challenge [1]. In this work, amphiphilic AgNPs which can easily be dispersed in alcohols were synthesized. In the first step, poly(acrylic acid) stabilized AgNPs (PAA-AgNPs) were obtained by using hydrazine for silver nitrate reduction. Amphiphilic AgNPs were then prepared by modifying PAA-AgNPs with 3- morpholinopropylamine (MPA) via an amidation reaction. The stability of the AgNP suspensions in several solvents was investigated by UV-Vis and zeta-potential measurements. Dynamic light scattering measurements revealed that the amphiphilic AgNPs had an average size of less than 10 nm, which did not pose a risk of clogging printer nozzles. A conductive ink formulation consisting of a 5 wt % AgNP dispersion in a 50 vol % water/ethanol mixture was selected for inkjet printing. Viscosity, surface tension and density of the ink were optimized to match the printer requirements. Multiple layers were printed on PET sheets and electrical properties of the printed films were evaluated with a four-point probe. Photonic annealing (IPL) was used to improve the film conductivities, achieving sheet resistances below 1 Ω/sq.

The miniaturization and persistent presence of smart devices has led to their mass production, with digital inkjet printing technology standing out as a simple, fast, and economical manufacturing method. Such an approach requires the formulation of an electrically conductive ink based on dissolving and stabilizing the functional material in a suitable solvent or solvent mixture. Due to its outstanding electrical conductivity and mechanical durability, intensive research has been focused on the manufacturing techniques of graphene. Presented here is a study on the preparation and optimization of graphene inks suitable for inkjet printing on a PET substrate. We have adopted a facile mechanochemical route for single and two layered graphene nanosheet fabrication, by melamine induced exfoliation in a planetary ball mill. Stability of the melamine intercalated graphene nanosheets (M-GNs) was evaluated in several solvents. Finally the M-GNs were dispersed in a mixture of water and ethanol with the aid of commercial polymeric dispersants Solsperse 20000 and 12000S at a concentration of 3 mg/mL. Surface tension, viscosity and density of this ink were optimized to match the inkjet printer requirements. Dynamic light scattering measurements revealed an adequate average particle size of 200 nm. Multiple layers of the ink were printed and electrical properties of the samples were evaluated. The printed features were exposed to intense pulsed light (IPL), thereby lowering their sheet resistance by an order of magnitude.

The main goal of this study was to examine the effect of calcium phosphate coating (CaP coating) on the corrosion resistance of titanium alloy, Ti– 6Al–7Nb, commercially used as an implant material in orthopedic devices. In addition to enabling osseointegration, the CaP coating forms a kinetic barrier to the electrochemical corrosion reaction, thus protecting the material from corrosion- induced degradation. This further increases the biocompatibility of the implant material. The CaP coating was deposited to the Ti–6Al–7Nb alloy by the electrochemical cathodic deposition method. Electrodeposition of the calcium phosphate film was performed from an aqueous solution of Ca(NO3)2 and NH4H2PO4 salts and film formation parameters were investigated using cyclic voltammetry (CV). Electrochemical characterization of the Ti–6Al–7Nb alloy in simulated body fluid, Hank’s solution was performed before and after the surface modification. The following electrochemical experimental techniques were used: electrochemical impedance spectroscopy (EIS) and linear polarization (LP) in the narrow (±20 mV vs. open circuit potential) and in the wide (±200 mV vs. open circuit potential) potential range at a scan rate of 0.1667 mV/s. The morphology and microstructure of CaP deposit obtained was characterized by scanning electron microscopy (SEM) and chemical composition was assessed by attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR).

Svrha ovog rada bila je ispitati učinak kalcij- fosfatne biokeramičke prevlake (CaP-prevlaka) na korozijsku otpornost titanijeve legure s aluminijem i niobijem, Ti–6Al–7Nb koja se komercijalno upotrebljava kao implantni materijal u ortopedskim uređajima. Naime, osim što omogućuje oseointegraciju, CaP-prevlaka čini kinetičku barijeru za odvijanje elektrokemijske korozijske reakcije te tako štiti materijal od degradacije uzrokovane korozijom. Time se također povećava biokompatibilnost implantnog materijala. Kalcij-fosfatna prevlaka nanesena je na uzorak Ti– 6Al–7Nb elektrokemijskom metodom katodne depozicije. Elektrodepozicija filma kalcijevog fosfata provedena je iz vodene otopine Ca(NO3)2 i NH4H2PO4. Formiranje filma provedeno je u trajanju od 1 h pri dva potencijala elektrodepozicije odabranih na temelju rezultata cikličke voltametrije. Provedena je elektrokemijska karakterizacija Ti– 6Al–7Nb legure u simuliranoj fiziološkoj otopini (Hanksovoj otopini). Na taj su način određena elektrokemijska korozijska svojstva legure, koja su uspoređena prije i nakon površinske modifikacije. Korištene su sljedeće elektrokemijske eksperimentalne tehnike: elektrokemijska impedancijska spektroskopija (EIS), linearna polarizacija u širokom, te linearna polarizacija u uskom rasponu potencijala u odnosu na potencijal otvorenog kruga. CaP depozit dodatno je okarakteriziran metodom optičke mikroskopije. Interpretacijom impedancijskih spektara određeno je kako je površina nemodificirane Ti–6Al–7Nb legure prevučena spontano formiranim filmom titanijevog(IV) oksida, TiO2, koji se sastoji od dva dijela, vanjskog (poroznog) te unutarnjeg (barijernog). Ustanovljeno je kako je za korozijsku otpornost nemodificirane legure odgovoran barijerni dio filma TiO2. Temeljem impedancijskih spektara modificiranih uzoraka određeno je kako se površinski film sastoji od dva dijela: vanjskog, koji čini CaP depozit isprepleten s poroznim slojem TiO2 ; te unutarnjeg, koji se sastoji od barijernog TiO2. Temeljem vrijednosti otpornih komponenata zaključuje se kako CaP depozit doprinosi poboljšanju polarizacijskog otpora Ti–6Al–7Nb legure.

Ovaj rad bavi se modificiranjem te ispitivanjem plošnih all–solid ionsko–selektivnih elektroda. Elektrode su prireĊene tehnikom printanja na plastificiranoj podlozi pri ĉemu je kao tinta korišteno nanosrebro. Modifikacije su provedene u 1 mM i 2 mM otopini kalijeva heksacianoferata(II) podešene ionske jakosti pomoću 0,1 M otopine NaNO3, a ukljuĉuju kemijsko i elektrokemijsko oslojavanje metalne elektrode slabotopljivom soli srebrovog heksacianoferata(II). Kemijsko oslojavanje provedeno je namakanjem elektrode 72 sata u neutralnoj, odnosno 2 sata u kiseloj otopini K4[Fe(CN)6], dok je elektrokemijska modifikacija provedena cikliĉkom voltametrijom i potenciostatski. Tako pripremljene Ag|Ag4[Fe(CN)6] elektrode ispitivane su potenciometrijski u neprotoĉnim ćelijama pomoću niza standardnih otopina podešene ionske jakosti. Odziv na ione srebra odreĊivan je pomoću otopina AgNO3 u 0,1 M NaNO3, dok je odziv na heksacianoferate(II) mjeren u otopinama K4[Fe(CN)6] u 0,1 M NaNO3. Odzivi dobiveni za Ag+–ione su linearni u koncentracijskom rasponu od 10^–1 do 10^–7 M, a za heksacianoferat(II) u koncentracijskom rasponu od 10^–1 do 10^–4 M. This work deals with modifying planar all–solid ion–selective electrodes and then using those in potentiometric measurements. Electrodes were manufactured by ink–jet printing technology on plastic substrate and then modified in 1 mM and 2 mM solutions of potassium hexacyanoferrate(II) prepared in 0,1 M solution of NaNO3. Modifications include chemical and electrochemical coating of metal electrode with a metal salt. One chemical modification was made by dipping the electrode in pH neutral K4[Fe(CN)6] solution for 72 hours, and the other one by dipping the electrode for 2 hours in acid solution of K4[Fe(CN)6]. Electrochemical modification of the electrode was done by cyclic voltammetry and at fixed potential. These Ag|Ag4[Fe(CN)6] electrodes were then used for potentiometric measurements in standard solutions of AgNO3 in 0,1 M NaNO3, for the determination of silver cations. Standard solutions of K4[Fe(CN)6] prepared in 0,1 M NaNO3 were used for measurement of hexacyanoferrates(II) concentrations. The linear response was obtained for silver ions in concentration range of 10^–1 – 10^–7 M and of 10^–1 – 10^–4 M for hexacyanoferrates(II).