Μm Cm2 Research Articles

Chitosan-assisted self-assembly of flower-shaped ε-Fe2O3 nanoparticles on screen-printed carbon electrode for Impedimetric detection of Cd2+, Pb2+, and Hg2+ heavy metal ions in various water samples

This study focuses on the fabrication of a novel sensing platform on a screen-printed carbon electrode, modified by a combination of hydrothermally synthesized iron dioxide (ε-Fe2O3) nanoparticles and Chitosan (CS) biopolymer. This unique organic-inorganic hybrid material was developed for Electrochemical Impedance Spectroscopy (EIS) sensing, specifically targeting heavy metal ions that include Hg2+, Cd2+, as well as Pb2+. The investigation encompassed a comprehensive analysis of various aspects of the prepared Fe2O3 and CS/ε-Fe2O3 nanocomposites, including phase identification, determination of crystallite size, assessment of surface morphology, etc. CS/ε-Fe2O3 was drop-casted and deposited on the Screen-Printed Electrode (SPE). The resulting sensor exhibited excellent performance in the precise and selective quantification of Hg2+, Cd2+, and Pb2+ ions, with minimal interference from other substances. The fabricated sensor exhibits excellent performance as the detection range for Hg2+, Cd2+, and Pb2+ ions linearity is 2–20 μM, sensitivity, and LOD are 243 Ω/ μM cm2 and 0.191 μM, 191 Ω/μM cm2, and 0.167 μM, 879 Ω/ μM cm2, and 0.177 μM respectively. The stability of the CS/ε-Fe2O3/SPE electrode is demonstrated by checking its conductivity for up to 60 days for Hg2+, Cd2+, and Pb2+ ions. The reusability of the fabricated electrode is 14 scans, 13 scans, and 12 scans for Hg2+, Cd2+, and Pb2+ ions respectively. The findings indicate the successful development of an innovative CS/ε-Fe2O3 electrode for the EIS sensing platform. This platform demonstrates notable potential for addressing the critical need for efficient and sensitive EIS sensors capable of detecting a range of hazardous heavy metal ions, including Hg2+, Cd2+, and Pb2+.

Covalent-organic framework/carbon nanotubes for electrochemical detection of o-nitrophenol

Covalent organic frameworks (COFs) have aroused much attention as candidate materials for constructing electrochemical sensors. However, their inherent low conductivities have limited their sensing applications. Here, a novel COF/carbon nanotubes (CNTs) composite is prepared via a straightforward ultrasonic method, incorporating amino-functionalized CNTs (NH2-CNTs) into COF composed of 1, 3, 5-benzenetricarboxaldehyde and 1,4-diaminobenzene. The resulting COF/NH2-CNTs composite exhibits high specific surface area, improved conductivity, fast electron transfer capability due to the high porosity of COF, the introduction of NH2-CNTs, and the conjugate interaction between CNTs and COF. The proposed COF/NH2-CNTs-based sensor offers an amplified current toward the electrochemical sensing of o-nitrophenol (o-NP). Notably, the sensor exhibits a wide linear detection range (0.1–100 and 100–1000 μM), a high sensitivity (8.66 and 1.44 μA/(μM cm2)), and a very low detection limit (0.03 μM). Moreover, it is successfully applicable in the quantitative analysis of o-NP in lake water samples with satisfactory recoveries (97.0–105.3 %). This work not only demonstrates the viability of COF-based sensors for the trace-level detection of nitrobenzene contaminants but also enriches the variety of COF-based sensing materials.

Nonenzymatic Sensor Based on Polythiophene/Titanium Dioxide (PTh/TiO2) Composite for the Determination of Malathion in Water

This study presents a novel nonenzymatic pesticide sensor utilizing a polythiophene/TiO2 (PTh/TiO2) film deposited on a glassy carbon (GC) electrode as the working electrode. The thiophene monomer was polymerized onto TiO2 by cyclic voltammetric method in the range of 0.0-2.5 V with 15 cycles at room temperature. The prepared electrode was used for the sensitive and selective detection of malathion thus providing the basis for facile electrochemical quantification. The surface morphology and crystal structure of the (PTh/TiO2) film were studied by SEM and XRD. FTIR was used for the structural analysis of (PTh/TiO2) film. FTIR results indicated that the PTh/TiO2composite structure was formed. The smooth surface morphology of PTh/TiO2 was supported by SEM results. XRD analysis verified that PTh is covered on TiO2 particles. The crystal phase of TiO2 was changed to amorph state after PTh modification. Additionally, the electrochemical characterization of polymer film and its response to malathion was examined by the CV method. Under optimized operational conditions, the response of the pesticide sensor was measured by CV in the range of -1 to 2.3 V versus the Ag/AgCl reference electrode due to the electrooxidation of malathion. The analysis focused on current values at -0.73 V, where the reduction of the PTh/TiO2 system occurred upon the addition of known amounts of malathion. The PTh/TiO2 composite film was sensitive to malathion in a linear range from 9.9 ppm to 436 ppm. The sensitivity was calculated as 57.5 μA/ µM cm2 whereas the detection limit was calculated as 7.45 µM. The maximum reaction rate was estimated as 767 μA. The developed sensor also showed good selectivity and reproducibility. The nonenzymatic pesticide sensor was successfully applied to detect malathion in tap water with at least 90% recovery.

Reduced graphene oxide decorated with poly(diallyldimethylammonium chloride) for sensitive detection of acetaminophen in water and human urine samples

In this work, we have developed an efficient electrochemical sensor using screen-printed carbon electrodes (SPCE) modified by reduced graphene oxide-poly(diallyldimethylammonium chloride) (i.e., rGO-PDDA) composites to detect acetaminophen with superior sensitivity and excellent selectivity. The polymerization process resulted in a uniform PDDA coating along with chemically reducing rGO sheets in the presence of hydrazine, thus producing the rGO-PDDA composites. Adopting the Taguchi method with analysis of variances, an optimal parameter set (i.e., rGO/PDDA ratio 1:20, amplitude 100 mV, pulse width 100 ms, and pulse period 0.3 s) with a confidence level of 95% was derived for designing the electrochemical sensors. Accordingly, a linear fit of the signal output versus acetaminophen concentration (r2: 0.9973) was obtained in a wide concentration range (0.794–68.9 μM). The sensitivity of acetaminophen on the SPCE reaches as high as 1.76 μA/(μM cm2) with an ultralow detection limit of 0.0773 μM. The sensitivity of the prepared sensor was also confirmed through exploring the detection of acetaminophen on the SPCE with five interfering species including urea, p-cresol, ascorbic acid, ibuprofen, and 4-aminophenol. The prepared electrode was successfully applied for detecting acetaminophen level in human urine samples. We believed that the robust design of SPCE modified with rGO-PDDA composites demonstrated in this work enables engineering high-performance sensors with superior sensitivity, low detection limit, wide concentration range, and enhanced selectivity toward acetaminophen at ultralow concentrations.

Electrochemical platform based on molecularly imprinted polymer with zinc oxide nanoparticles and multiwalled carbon nanotubes modified screen-printed carbon electrode for amaranth determination.

Anovel electrochemical platform for amaranth determination has been developed using a rapid, easy, inexpensive, and portable molecularly imprinted polymer technique. The MIP platform was fabricated by electropolymerizing melamine as monomer in the presence of amaranth as template on the surface of ZnO-MWCNT/SPCE. Then, amaranth was completely eluted, leaving imprinted cavities in the polymeric film that could effectively recognize amaranth in solution. The electrochemical platform based on a molecularly imprinted polymelamine was analyzed by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Under optimum conditions, the developed MIP/ZnO-MWCNT/SPCE platform can be properly used for amaranth determination, with high sensitivity of 96.2 µA µM cm-2, two linear concentration ranges (0.01 to 1µM and 1 to 1000µM) and a low limit of detection of 0.003µM. The anodic peak potential of amaranth was found to be 0.73V. Additionally, the polymelamine MIP films specifically recognize amaranth molecules, making it possible to detect amaranth in a complex solution with high selectivity, excellent repeatability, reproducibility, and stability. The MIP/ZnO-MWCNT modified screen-printed carbon electrode was successfully applied to determine amaranth in pharmaceutical and water samples, with recovery values ranging from 99.7 to 102% and RSD% values less than 3.2%.

A CTAB-assisted PANI-MoS2 nanosheet flower morphology for the highly sensitive electrochemical detection of hydrazine.

In this work, cetyl trimethylammonium bromide (CTAB)-assisted polyaniline-molybdenum disulfide (CPANI-MoS2) nanosheets with a flower morphology have been synthesized through in situ polymerization and a hydrothermal method. The composite was analyzed for structural modification through X-ray diffraction (XRD) to examine chemical changes and the presence of functional groups via Fourier transform infrared (FTIR) and Raman spectroscopy techniques. The surface morphology was identified by field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HR-TEM) techniques. The CPANI-MoS2 nanosheet glassy carbon electrode (GCE) offers a novel strategy for the electrochemical detection of carcinogenic hydrazine. The cyclic voltammetry (CV) curve demonstrated a quasi-reversible behaviour with a high-surface area. Furthermore, differential pulse voltammetry (DPV) analysis of hydrazine detection showed a wide linear range from 10 μM to 100 μM, a low limit of detection of 0.40 μM, and a high sensitivity of 7.23 μA μM cm-2. The determination of hydrazine in a water sample and the recovery percentage were found to be 100.31% and 103.73%, respectively. The CPANI-MoS2 nanosheet GCE significantly contributed to the high electroanalytical oxidation activity due to the CTAB surfactant modifying the flower-like nanosheet morphology, which enables the easy adsorption of hydrazine analyte species and exhibits a high current rate with a rapid detection response.

Lanthanum tin oxide-modified sensor electrode for the rapid detection of environmentally hazardous insecticide carbaryl in soil, water, and vegetable samples

The growing population and global food demands have encouraged the use of pesticides to increase agricultural yields; however, the irrational use of pesticides threatens human health and the environment. Carbaryl (CRBL) is the most widespread insecticide and severely affects soil, water systems, and human health. Thus, it is crucial to monitor CRBL residues in the environment and vegetable samples. This study reports the rapid and sensitive electrochemical detection of CRBL based on a pyrochlore-type lanthanum tin oxide (LSO) nanoparticles (NPs)-modified screen-printed carbon electrode (SPCE). A low-temperature hydrothermal method was employed to prepare the LSO NPs. The structural properties of the LSO NPs were characterized by X-ray diffraction, Raman, and X-ray photoelectron spectroscopy analyses. The LSO NPs/SPCE demonstrated good electroanalytical performance for CRBL detection, with a low detection limit of 0.4 nM (0.08 µg/L) and a sensitivity of 1.05 µA/(µM cm2). Furthermore, the LSO NPs/SPCE exhibited high selectivity among highly interfering carbamate and organophosphorus pesticides, which share similar mechanisms of action. Additionally, the LSO NPs/SPCE sensor achieved > 90% recovery for the detection of CRBL in soil, water, and vegetable samples, thus verifying its suitability for the rapid detection of CRBL.

Bioconjugates of mercaptocarboxylic acids functionalized AuNP and superoxide dismutase for superoxide electrochemical monitoring.

Theuse of gold nanoparticles/superoxide dismutase (AuNP/SOD) bioconjugates is described as building blocks in SOD biosensor development for the quantification of superoxide in cell culture media. AuNP functionalization with 11-mercaptoundecanoic acid (MUA) and 4-mercaptobenzoic acid (MBA) (AuNPMUA and AuNPMBA) was used to improve SOD immobilization through EDC/NHS coupling using their -COOH terminus, leading to the formation of more stable bioconjugates. AuNP and AuNP/SOD bioconjugates were characterized by SEM to determine their size and morphology, UV-Vis for optical properties, FT-IR, and Raman spectroscopies for chemical functional group analysis and EDX for elemental analysis. Electrochemical methods were used to characterize the Au/AuNP-modified electrodes. For the optimization of the biosensor architecture, different AuNP/enzyme bioconjugates were prepared by varying the amount of both enzyme and AuNP, as well as their incubation time. Finally, the biosensors incorporating the bioconjugates were characterized by fixed potential amperometry and voltammetric analysis in order to establish the enzymatic mechanism and to elucidate the best biosensor architecture for monitoring superoxide in cell culture media. The best sensitivity value for superoxide detection corresponded to 41.2 nA µM cm-2, achieved by a biosensor based on AuNPMBA/SOD bioconjugates monitored through fixed potential amperometry at 0.3V vs. Ag/AgCl, with a limit of detection of 1.0µM, and overall very good operational stability, maintaining 91% of the initial sensitivity after 30days. Finally, the optimized biosensor was employed for the quantification of successive additions of superoxide in cell culture media, with excellent recovery values.

Characterization of a synthetic zinc-chelating peptide from sea cucumber (Stichopus japonicus) and its gastrointestinal digestion and absorption in vitro.

Zinc absorption in intestinal system could be strongly affected by the gastrointestinal digestion and absorption of zinc-chelating peptides serving as zinc carriers. In this study, a novel zinc-chelating sea cucumber synthetic peptide (SCSP) was synthesized to estimate its gastrointestinal digestion and promotive effect of zinc absorption in vitro. Analysis of isothermal titration calorimetry suggested that the binding of SCSP and zinc (N ≈ 1) was exothermic, with relatively weak binding affinity (K=1.0 × 10-3 mol L-1 ). The formation of SCSP-Zn complexes brought morphological changes to the peptides confirmed by scanning electron microscopy (SEM), which also indicated 6.88% of the existence of zinc element. In addition, the SCSP-Zn complexes remained stable under simulated human gastrointestinal digestion. In an in vitro study, the SCSP-Zn complex could successfully transport through the intestinal membrane in the model of everted rat gut sacs (nearly 7.5μM cm-2 ) as well as Caco-2 cells where the zinc transport reached 0.0014 mg mL-1 carried by SCSP. Fluorescence staining experiments revealed free zinc accumulation inside the tissues and cells treated with the SCSP-Zn complex. The chelation SCSP-Zn had the promotion ability of zinc absorption in vitro and ex vivo experiments, which suggested a theoretical basis for the design and production of effective zinc chelating peptides as zinc carriers to improve zinc bioavailability. © 2022 Society of Chemical Industry.

HRP modified pulse laser ablated ZnO nanostructure for H2O2 sensing

Biosensor for the detection of hydrogen peroxide (H2O2) has been prepared by immobilizing horseradish peroxidase (HRP) enzyme using physical adsorption technique on zinc oxide (ZnO) nanostructures. The (002) oriented ZnO nanostructures as confirmed by X-ray diffraction, were successfully grown on indium tin oxide (ITO) coated glass substrate by pulsed laser ablation (PLA) without using any catalyst. The Nafion solution was added onto HRP/ ZnO/ ITO bio-electrode to form a tight membrane on the surface before carrying out bio-sensing measurements by electrochemical analyzer. The electrochemical studies reveal that the prepared bio-electrode HRP/ZnO/ITO is highly sensitive to the detection of H2O2 over a wide range of concentration with a linear range from 2.5 μM to 100 μM with the limit of detection 0.2 μM and sensitivity of 0.034 µA/ µM cm2. The higher sensitivity attributed to larger surface area of ZnO nanostructure for effective loading of HRP besides its high electron communication capability. A relatively low value of the enzyme’s kinetic parameter (Michaelis-Menten constant, Km) of 0.166 μM indicates enhanced enzyme affinity of HRP to H2O2. The reported biosensor may be useful for various applications in bio-sensing, clinical, food and beverage industry.

Bio-PEDOT: Modulating Carboxyl Moieties in Poly(3,4-ethylenedioxythiophene) for Enzyme-Coupled Bioelectronic Interfaces.

Modulation of chemical functional groups on conducting polymers (CPs) provides an effective way to tailor the physicochemical properties and electrochemical performance of CPs, as well as serves as a functional interface for stable integration of CPs with biomolecules for organic bioelectronics (OBEs). Herein, we introduced a facile approach to modulate the carboxylate functional groups on the PEDOT interface through a systematic evaluation on the effect of a series of carboxylate-containing molecules as counterion dopant integrated into the PEDOT backbone, including acetate as monocarboxylate (mono-COO-), malate as dicarboxylate (di-COO-), citrate as tricarboxylate (tri-COO-), and poly(acrylamide-co-acrylate) as polycarboxylate (poly-COO-) bearing different amounts of molecular carboxylate moieties to create tunable PEDOT:COO- interfaces with improved polymerization efficiency. We demonstrated the modulation of PEDOT:COO- interfaces with various granulated morphologies from 0.33 to 0.11 μm, tunable surface carboxylate densities from 0.56 to 3.6 μM cm-2, and with improved electrochemical kinetics and cycling stability. We further demonstrated the effective and stable coupling of an enzyme model lactate dehydrogenase (LDH) with the optimized PEDOT:poly-COO- interface via simple covalent chemistry to develop biofunctionalized PEDOT (Bio-PEDOT) as a lactate biosensor. The biosensing mechanism is driven by a sequential bioelectrochemical signal transduction between the bio-organic LDH and organic PEDOT toward the concept of all-polymer-based OBEs with a high sensitivity of 8.38 μA mM-1 cm-2 and good reproducibility. Moreover, we utilized the LDH-PEDOT biosensor for the detection of lactate in spiked serum samples with a high recovery value of 91-96% and relatively small RSD in the range of 2.1-3.1%. Our findings provide a new insight into the design and optimization of functional CPs, leading to the development of new OBEs for sensing, biosensing, bioengineering, and biofuel cell applications.

Ultrasmall Au(0) Inserted Hollow PCN-222 MOF for The High-Sensitive Detection of Estradiol.

Here, the effect of morphology on the electrocatalytic activity of metal-organic framework (MOF) was investigated. Post synthetic gold (Au) insertion was done into hollow PCN-222 (HPCN-222) and solid PCN-222 (SPCN-222) frameworks by a simple hydrothermal method. The crystalline nature, chemical composition, and morphologies of the synthesized MOFs were characterized by PXRD, XPS, and TEM. Electrochemical characterizations were done by cyclic voltammetry and electrochemical impedance spectroscopy. The excellent electrocatalytic activity of highly small-sized Au(0) with the enhancement of electrical conductivity through a hopping mechanism combined with a hollow structure and high surface area in the HPCN-222 MOF hugely alters the electrochemical properties. Overall, a better electrocatalytic surface area, charge transfer coefficient, and catalytic activity were generated at the modified electrode. The hollow structure MOF showed better electrocatalytic activity than solid structured MOF. The AuHPCN-222 modified glassy carbon electrode (AuHPCN-222/GCE) electrochemical sensor was employed for the analytical analysis of estradiol (ED) in an optimum experimental condition. AuHPCN-222 showed selective and better electrocatalytic activity toward ED than GCE. The differential pulse voltammetric measurements by the fabricated sensor showed two linear determination ranges for ED; those are 0.01-1 and 1-220 μM. The measured limit of detection (m-LOD) was found to be 0.5 nM with the highest sensitivity of 2.2 μA μM cm-2. The analytical performances for the detection of ED in human urine and serum samples were done with reasonable recoveries (98%-103%) using the standard addition method. Also, the sensor showed better reproducibility and repeatability with stability.

Fabrication of Nanostructured Pd Thin Films Using Aerosol-Assisted Chemical Vapor Deposition for the Nonenzymatic Electrochemical Detection of H2O2

An improved and facile aerosol-assisted chemical vapor deposition (AACVD) process for the production of palladium thin film on indium tin oxide (PdNP-ITO) electrodes was described and applied for the electrochemical detection of hydrogen peroxide (H2O2). The detailed characterization of the films by X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS) analysis proved the high crystallinity and phase purity of the nanosized metallic palladium films without the evolution of any elemental impurities from the precursor compound. The as-prepared electrodes were used for nonenzymatic amperometric H2O2 detection via electrochemical reduction. The LOD was 40.8 nM with a high sensitivity of 760.84 μA/(μM cm2). From the experimental scan rate variation analysis, the reduction of H2O2 on the PdNP-ITO electrode surface was determined to be adsorption controlled. For this process of adsorption, we calculated the number of elect...

A Porous TiO2-Based Two-Layer Anode with Improved Performance Manufactured By Large Area Layer-By-Layer Spray Processing

Although porous TiO2 particles (200 nm) with 30-50 nm internal pores can exhibit a high power response because of shortened Li+ ion diffusion lengths, an anode consisting of these porous TiO2 particles-only exhibited a low overall volumetric capacity due to a low tap density. On the other hand, TiO2 nanoparticles (20 nm) can exhibit a high volumetric capacity because of a relatively high tap density, but an anode consisting of these TiO2 nanoparticles-only exhibited a relatively low power response due to restricted Li+ ion mobility. To exploit optimally the different intrinsic advantages of both types of TiO2, a rational design of a two-layer anode structure was developed to locate the porous TiO2 particles in the inner layer of the anode (nearer to the current collector but further away from the separator) where Li+ ion diffusion is usually limited, while the TiO2 nanoparticles were located in the outer layer of the anode (nearer to the separator but further away from the current collector) where Li+ ion diffusion is comparatively unrestricted, as shown in Figure 1(a). In both of the layers, an interconnected multi-wall carbon nanotube (MWNT) scaffold decorated with the TiO2 particles was used to ensure electrical connectivity and prevent TiO2 agglomeration. The reversible volumetric capacity of the two-layer anode was 232.3 mAh cm-3 at a slow (dis)charge rate of 0.1 C, slightly higher than 220.9 mAh cm-3 for the anode consisting of TiO2 nanoparticles-only, and much higher than 104.5 mAh cm-3 for the anode consisting of porous TiO2 particles-only. Moreover, the volumetric capacity retention of the two-layer anode, as the (dis)charge rate was increased from 0.1 to 4 C, was similar to 38.5% for the porous TiO2 anode, and much higher than 7.1% for the TiO2 nanoparticles. Consequently, the two-layer anode structure maintained the intrinsic advantages of both types of the nanostructured TiO2. The two-layer electrode structure was made possible by a flexible and scalable layer-by-layer (LbL) atomisation spray processing technique developed in Oxford University, as shown in Figure 1(b). The LbL spray processing method allowed flexible design of nano-scale active materials arrangements at the meso-scale electrode structure. The spray processing method has a fast production rate of ~10 µm cm-2 min-1, capable of making 200 nm – 110 µm thick and up to 1 m x 20 cm large area electrodes using a drum coater, and is thus attractive for complementing existing slurry casting methods. Finally, direct experimental measurements by in-depth X-ray photoelectron spectroscopy (XPS) profiling of post-mortem anodes were performed to investigate Li+ ion transfer dynamics through the thickness of various structured anodes. Differences in the spatial distribution of Ti4+ to Ti3+ states were entirely consistent with the different anode designs and performance. This work shows how it is now possible to better design and tailor layered electrode structure to improve volumetric capacity and rate capability compared with conventional, randomly mixed electrodes. Figure 1

Fabrication of Ni–Fe2O3 magnetic nanorods and application to the detection of uric acid

Doping of Ni into Fe2O3 lattices has been achieved by co-precipitation followed by thermal decomposition method. The structural, morphological, and magnetic properties of the fabricated samples were investigated by X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared (FT-IR) spectroscopy, UV-visible absorption (UV-vis) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The results reveal that the Ni is well doped within the lattices of Fe2O3. The Ni dopant suppresses the formation of more stable α-Fe2O3 at higher calcination temperature. Further, the Ni-doped Fe2O3 nanoparticles were used to fabricate an electrochemical sensor (Ni–Fe2O3/GCE) for the detection of uric acid (UA) in biological conditions by cyclic voltammetry (CV) and chronoamperometry (CA). It was found that 5%Ni–Fe2O3/GCE exhibits best response towards UA with less positive potential and larger current response. Furthermore, the sensor gives good linear current response in the concentration range of 6.6 to 112.4 μM with the higher sensitivity of 0.849 μA (μM cm2)−1. Such fabricated sensors are appropriate for newly emerging non-enzymatic electrochemical nanobiosensors.

Pulsed laser coating removal by detachment and ejection

The pulsed laser removal of paint coatings from substrates by detachment and ejection of the entire layer has been studied. The dependence of the removal efficiency on fluence, coating thickness and pulse duration has been examined. For weakly absorbing coatings on easily ablating substrates, efficiencies as high as 800 μm cm2 J-1 have been measured, i.e., more than two orders of magnitude higher than obtainable by surface ablation.

Holmium-YAG Laser ablation characteristics in calvarial lamellar and cortical bone: The role of water and tissue micro-architecture

The effect of tissue micro-architecture and water content on ablation rates in bone is examined. Precisely machined and prepared porcine calvarial lamellar and cortical bone were ablated with a Holmium-YAG laser (λ=2.1Μm). Lamellar and cortical bone differ substantially in their tissue micro-architecture. Both are porous hard tissues, which differ predominantly in size and distribution of pores within the bone matrix. These hard tissues were ablated under physiological (wet) and chemically dehydrated conditions. The ablation rates over the range of energy densities examined assumes many linear characteristics. Ablation rate (as a function of fluence) is considerably higher for dehydrated cortical bone (4.7Μm cm2 J−1) compared to fresh cortical bone (1.49Μm cm2 J−1). This trend is also observed in lamellar bone (2.31Μm cm2 J−1 for wet and 0.37Μm cm2 J−1 for dry). Under both physiological and dehydrated conditions, cortical bone was ablated faster. Mechanisms accounting for these observations are discussed.

Nitrocellulose as a self-developing resist with submicrometer resolution and processing stability

Nitrocellulose films have been shown to function as self-developing resist layers that are sensitive to both low energy ion bombardment by heavy ions such as Ar+ or Xe+ and to 193 nm UV radiation from a pulsed excimer laser. The resist develops at 0.6 μm s−1 for a beam of 2 keV Ar+ ions (1 mA cm−2), and has a sensitivity of ∼2 μm cm2 J−1 for ArF laser radiation, together with a demonstrated optical resolution of 300 nm. The decomposition products of the self-developing resist consist primarily of water, nitrogen, carbon monoxide, nitric oxide, and carbon dioxide. When exposed to light ions, electrons, ArF laser radiation at energy densities less than 20 mJ cm−2, or heat, the resist decomposes leaving a nonvolatile residue. The formation of this residue is believed to be responsible for the comparative stability of nitrocellulose under reactive ion etching. The reactive ion etching rate in CHF3 is about twice as fast for nitrocellulose as for SiO2. The etching rate can be reduced by the addition of volatile metal salts to the nitrocellulose, but this also reduces the rate of self-development produced by heavy ion bombardment.