Ultrafast Pulsed Laser Ablation Research Articles

High-speed, scanned laser structuring of multi-layered eco/bioresorbable materials for advanced electronic systems

Physically transient forms of electronics enable unique classes of technologies, ranging from biomedical implants that disappear through processes of bioresorption after serving a clinical need to internet-of-things devices that harmlessly dissolve into the environment following a relevant period of use. Here, we develop a sustainable manufacturing pathway, based on ultrafast pulsed laser ablation, that can support high-volume, cost-effective manipulation of a diverse collection of organic and inorganic materials, each designed to degrade by hydrolysis or enzymatic activity, into patterned, multi-layered architectures with high resolution and accurate overlay registration. The technology can operate in patterning, thinning and/or cutting modes with (ultra)thin eco/bioresorbable materials of different types of semiconductors, dielectrics, and conductors on flexible substrates. Component-level demonstrations span passive and active devices, including diodes and field-effect transistors. Patterning these devices into interconnected layouts yields functional systems, as illustrated in examples that range from wireless implants as monitors of neural and cardiac activity, to thermal probes of microvascular flow, and multi-electrode arrays for biopotential sensing. These advances create important processing options for eco/bioresorbable materials and associated electronic systems, with immediate applicability across nearly all types of bioelectronic studies.

Effect of dual-beam laser radiation for synthetic SnO2/Au nanoalloy for antibacterial activity

A facile synthetic method was reported to synthesis nanostructured alloy from SnO2/Au in just one step without further purification or washing by a dual ultra-fast pulsed laser ablation in liquid media technique. The dual ultra-fast technique was based on splitting the laser irradiation by beam splatter to produce two paths. Each path makes a laser ablation process on each target immersed in ultra-pure water. The physicochemical properties of the prepared sample were investigated by XRD, UV–visible spectrometer, TEM, and EDX. XRD technique showed the formation of crystalline structure from Au and SnO2, while UV-visible spectrometer showed the formation of the absorption peaks of SPR of Au and the metal oxide of SnO2, whereas TEM revealed the nanostructure formation of nanostructured alloy structure, but EDX confirmed that the formation alloy had the composition structure from Au and SnO2. Furthermore, its antibacterial activity showed the highly efficient against E. coli rather than Bacillus subtilis.

Upconversion Nanoparticles Synthesized by Ultrashort Pulsed Laser Ablation in Liquid: Effect of the Stabilizing Environment.

The distinctive feature of upconverting compounds to absorb and emit light in the near-infrared region has made upconverting nanoparticles of great interest in various application fields. Nevertheless, these colloids show a highly hydrophobic behavior, and therefore, the use of a proper stabilizing agent is necessary in most cases. Although few chemical techniques for colloid stabilization are available, it is still difficult to achieve a fully reproducible synthesis method for stable upconverting nanoparticle colloids. In this work, upconversion 18 %Yb:1 %Er:NaYF4 nanoparticles were produced by ultrafast pulsed laser ablation in a water and 2-[2-(2-methoxyethoxy)- ethoxy]acetic acid (MEEAA) environment to assess the stabilization effect of the surfactant on the nanoparticle colloid properties. The effects of the laser fluence and MEEAA concentration on the nanoparticles' properties were investigated by TEM, EDS, and emission spectra analyses. The results show that ultrashort pulsed laser ablation in liquid allows generating highly spherical nanoparticles with conserved stoichiometry and optical properties. Moreover, it is possible to obtain colloids with significantly higher stability and preserved optical properties by one-step PLAL processes directly in the MEEAA environment.

Abstract LB-191: Photoacoustic detection and imaging of single cancer cells with peptide-conjugated gold nanoparticles

Abstract Photoacoustic imaging (PAI), which is based on the conversion of light into sound, is an emerging, hybrid and noninvasive imaging modality with highly scalable resolution. PAI has shown tremendous potential in early tumor detection and imaging by providing structural, functional and metabolic information. But to date, most work has been focused on tumor detection at the macroscopic level (i.e. tissue, organ). For early tumor diagnosis, microscopic detection of individual cancer cells is highly desirable and of special significance. However, detection and imaging of single cancer cells using PAI is very challenging because most cancer cells are colorless, thus exhibiting little endogenous contrast. Gold nanoparticles (AuNPs), which have good biocompatibility, low toxicity and high optical absorption, are an exogenous contrast agent that can facilitate PAI of single cancer cells. In this study, we synthesized peptide-conjugated AuNPs to selectively target DU145 human prostate cancer cells, and employed a laser-scanning photoacoustic microscopy (PAM) to detect and image individual cells. The used AuNPs had an average diameter of 30 nm and were physically fabricated by ultrafast pulsed laser ablation of gold target in ultrapure water. Their surface chemistry was modified through a sequential conjugation process, in which a predetermined amount of thiolated PEG 5000 molecules and RGD peptides were successively bound to the AuNPs with quantitative control and high efficiency. After incubation with DU145 cells, the functionalized PEG-RGD-AuNPs were endocytosed with the help of membrane receptors and produced sharp absorption contrast. The internalized AuNPs generated strong photoacoustic signals after absorbing excitation laser and the signals were captured by a highly sensitive hydrophone to form cell images. Combing functional AuNPs and high-resolution PAM, we successfully detected and imaged single, live DU145 cancer cells. Though transparent, the cancer cells were visibly delineated by intracellular AuNPs and were clearly distinguishable. Moreover, to achieve optimum detection efficiency, we also studied the relationship between the density of RGD peptide and the amplitude of photoacoustic signal. Experimental results reveal that, although the amount of cellular uptake of AuNPs was proportional to RGD density (from radioactivity analysis using a Gamma counter), the amplitude of photoacoustic signal did not. Photoacoustic detection efficiency reached a maximum when the molar ratio of RGD peptides to AuNPs was approximately 1000. To our best knowledge, this is the first report on photoacoustic detection and imaging of specific cancer cells using peptide-conjugated AuNPs at single-cell resolution. By translating PAI from macro to micro, the work is expected to open a new avenue for early cancer detection, imaging, diagnosis and even treatment. Citation Format: Chao Tian, Wei Qian, Xia Shao, Zhixing Xie, Xu Cheng, Shengchun Liu, Qian Cheng, Bing Liu, Xueding Wang. Photoacoustic detection and imaging of single cancer cells with peptide-conjugated gold nanoparticles. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-191.

Femtosecond laser ablation of cadmium tungstate for scintillator arrays

Ultrafast pulsed laser ablation has been investigated as a technique to machine CdWO4 single crystal scintillator and segment it into small blocks with the aim of fabricating a 2D high energy X-ray imaging array. Cadmium tungstate (CdWO4) is a brittle transparent scintillator used for the detection of high energy X-rays and γ-rays. A 6W Yb:KGW Pharos-SP pulsed laser of wavelength 1028nm was used with a tuneable pulse duration of 10ps to 190fs, repetition rate of up to 600kHz and pulse energies of up to 1mJ was employed. The effect of varying the pulse duration, pulse energy, pulse overlap and scan pattern on the laser induced damage to the crystals was investigated. A pulse duration of ≥500fs was found to induce substantial cracking in the material. The laser induced damage was minimised using the following operating parameters: a pulse duration of 190fs, fluence of 15.3Jcm−2 and employing a serpentine scan pattern with a normalised pulse overlap of 0.8. The surface of the ablated surfaces was studied using scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy. Ablation products were found to contain cadmium tungstate together with different cadmium and tungsten oxides. These laser ablation products could be removed using an ammonium hydroxide treatment.

Design and development of novel screen-printed microelectrode and microbiosensor arrays fabricated using ultrafast pulsed laser ablation

A new generic platform for the development of microbiosensors combining screen-printing and ultrafast pulsed laser technologies has been developed, characterised and evaluated. This new platform consists of a layer of screen-printed carbon ink containing the enzyme and mediator, covered with an insulating layer formed from a dielectric screen printed ink. Microholes were drilled through the insulated layer by ultrafast pulsed laser ablation to generate the microbiosensor array. The geometry of the microelectrode array was evaluated by optical microscopy, white light surface profiling and scanning electron microscopy. The electrochemical behaviour of the microelectrode array was characterised by cyclic voltammetry and compared with macroelectrodes. The analytical performance of the microbiosensor array was evaluated with external counter and reference electrodes for hydrogen peroxide and glucose determination showing linearity up to 4mmolL−1 and 20mmolL−1 (360mgdL−1) respectively. The full screen printed three-electrode configuration shows linearity for glucose determination up to 20mmolL−1 (360mgdL−1). This study provides a new fabrication method for microelectrode and microbiosensor arrays capable for the first time to retain the activity of the enzymatic system after processing by pulse laser ablation.

Nanoparticle generation in ultrafast pulsed laser ablation of nickel

The process of particle generation during ultrafast pulsed laser ablation of nickel is investigated. Two types of particles with different sizes depending on the laser fluence are found, indicating different particle generation mechanisms. By limiting the laser fluence below a threshold of strong plasma formation, the large dropletlike particles can be eliminated. In addition, by supplying different background gases, various crystalline structures are obtained for the particles, including Ni∕NiO core/shell spheres and NiO cubes. This study provides evidence that ultrafast laser ablation can be a room temperature physical method for generating nanocrystals with a narrow particle size distribution.

Model description of surface charging during ultra-fast pulsed laser ablation of materials

We present a model describing the dynamical mechanisms responsible for generating fast ion ejection under ultra-short pulsed laser irradiation. The model is based on a simplified drift–diffusion approach describing the evolution of the laser-generated charge carriers, their transport, and the electric field generated as a result of quasi-neutrality breaking in the irradiated target. The importance of different processes in generating the non-thermal material-ejection mechanisms is discussed. A common frame is applied to dielectrics, semiconductors, and metals and different dynamical behaviour is observed. The modelling results are in good agreement with fs pump–probe studies and measurements of the velocity distributions of the emitted ions.

Electronic transport and consequences for material removal in ultrafast pulsed laser ablation of materials

Fast electronic transport is investigated theoretically based on a drift-diffusion approach for different classes of materials (metals, semiconductors, and dielectrics) under ultrafast, pulsed laser irradiation. The simulations are performed at intensities above the material removal threshold, characteristic for the ablation regime. The laser-induced charging of dielectric surfaces causes a subpicosecond electrostatic rupture of the superficial layers, an effect which, in comparison, is strongly inhibited for metals and semiconductors as a consequence of superior carrier transport properties.