This PDF file contains the front matter associated with SPIE Proceedings Volume 10738, including the Title Page, Copyright information, Table of Contents, Author listing, and Conference Committee listing.

Organic electrochemical transistors (OECTs) have gained considerable interest for applications in bioelectronics and neuromorphic computing. Their defining characteristic is the bulk-modulation of channel conductance owing to the facile penetration of ions into the (semi)conducting polymeric channel. In the realm of bioelectronics, OECTs have shown promise as amplifying transducers due to their stability in aqueous conditions and high transconductance. These devices can be fabricated in conformable form factors for in vivo stimulation/recording, and for cutaneous EEG and ECG recordings in human subjects. While past research has focused on the high transconductance operation of these devices, new materials present advantageous properties such as efficient sub-threshold switching. We report on a glycolated thiophene-based conducting polymer with sub threshold swing as low as 60 mV/decade, and on these materials’ integration as low power active sensing nodes for electrophysiological recordings.

Organic electronic materials are ideal for interfacing with biological systems in that they are biocompatible, bio-stable, and can be tailored for high electronic and ionic conductivity. These materials have been primarily applied to mammalian cells, tissues, and organisms as active components in bioelectronic devices for biomedical applications. Recently we interfaced organic electronic materials with plants. Plants are complex biological organisms and comprise our primary source of food, but are also a source of oxygen, renewable energy, materials, medicines and regulators of the ecosystem. We used water-soluble conducting polymers and oligomers that can self organize or polymerize in vivo, with the plant acting as the catalyst and template for the chemical reaction. We demonstrated analogue and digital circuits manufactured in the organs of a plant as well as supercapacitors for energy storage. Our latest findings show the organic electronic materials organising and forming conductors in parallel with the growth of the plant, resulting in a bio-hybrid system. In addition we are using bioelectronic devices to sense and actuate plant functions. We are applying devices such as ion pumps and organic electrochemical transistors to plants in order to control growth, transpiration and sense molecules related to photosynthesis. In this talk, I will present our recent advancements and discuss potential applications of our technology.

Polymer semiconductors have become increasingly popular in electrochemical transistors because of their high transconductance, simple fabrication for flexible devices, and compatibility with aqueous environments. These materials form highly nanostructured films, yet to date there are few studies investigating the interplay between ionic transport and nanoscale morphological properties. In this work, we show that in situ electrochemical strain microscopy (ESM) in aqueous electrolytes can directly probe local variations in polymer devices by measuring the sub-nanometer volumetric swelling in the film upon ion diffusion. These data indicate that areas of lower elastic modulus are correlated with higher ion permeability and thus greater volumetric response, which we attribute to the polymer being more amorphous and less densely packed in these regions. Indeed, this response is also sensitive to the anion present in the electrolyte, with the anion size affecting both the magnitude in ESM as well as having a strong effect on mobility. These data suggest that balancing the high hole mobility of crystalline materials with the ionic mobility in more amorphous materials can result in better performing organic electrochemical transistors across a wider range of electrolytes. Following this approach, we show evidence that anisotropic polymer structures underneath an active ionic transport layer can provide enhanced transconductance over conventional single-component materials by balancing a highly crystalline polymer with an amorphous ionic transport layer. These data show that in situ scanning probe microscopy techniques can provide meaningful pathways for improving rational design of organic electrochemical transistors.

Organic photodiodes (OPDs) have in recent years reached a level of performance comparable to their inorganic counterparts. Using additives like PMMA, we were able to tune the transparency and viscosity of a P3HT:PCBM photoactive blend while at the same time achieving a two-fold enhancement of the detection speed. Furthermore, we have developed approaches towards the digital realization of image sensors using aerosol jet printing and a direct-printed patterning technique utilizing the self organization of functional inks. These techniques allow for a reproducible deposition of multilayer devices with high registration accuracies and feature sizes down to a few microns. We present a comprehensive electrical and optical characterization of these printed image sensors. The devices exhibit specific detectivities of >1E12 Jones over a broad wavelength range (400-750 nm) and maximum responsivities of 0.25 A/W. An entirely printed matrix image sensor composing of 256 individual pixels with an individual active area of ≈250 μm × 300 μm was fabricated.

Wearable sensors enable the continuous monitoring of various physiological conditions of individuals without constraints on time and place. Primary vital signs of human body such as; heart rate (HR), Oxygen saturation (SpO2) and respiration rate, can be extracted from the PPG signal. In comparison to conventional inorganic based sensors, the use of organic semiconductor-based devices opens the possibility of devising inexpensive, lightweight, flexible sensors. Reflection-mode PPG sensors overcome the limitations posed by transmission-mode PPG sensor as it can be positioned anywhere on the body. The state of art has not exploited the reflection-mode of PPG sensors extensively, as opposed to transmission-mode. In this work, we have fabricated reflection mode PPG sensor, which comprises of a red (631 nm) organic light emitting diode (OLED) (EQE = 8%) and organic photodetector (OPD) (EQE =47 %) on the same substrate. With motivation to improve the existing PPG sensing technologies, OLED and OPD performances were optimized on a single substrate. Further, we have estimated the best pattern and optimal distance between OLED and OPD in order to maximize signalnoise ratio and lower the power consumption of the device. An analog circuit is designed to read out PPG signals. For realtime pulse monitoring, the signals were sent via a Bluetooth interface to the computer. In summary, a low cost, organic based sensor is developed to detect the heart rate with wireless enabled data monitoring. Our device displayed promising results with 1.5 % error in the heart rate measurement compared to the commercial reference.

Neuromorphic devices and architectures offer novel ways of data manipulation and processing, especially in data intensive applications. At a single device level, various forms of neuroplasticity have been emulated over the past years, mainly with inorganic devices. The implementation of neuroplasticity functions with these devices also enabled applications at a circuit level related to machine learning such as feature or pattern recognition. Although the field of organic-based neuromorphic devices and circuits is still at its infancy, organic materials may offer attractive features for neuromorphic engineering. Over the past years for example, a few simple neuromorphic functions have been demonstrated with biological substances and bioelectronic devices. In this work various neuromorphic devices will be presented that are based on organic mixed conductors, materials that are traditionally used in organic bioelectronics. A prominent example of a device in bioelectronics that exploits mixed conductivity phenomena is the organic electrochemical transistor (OECT). Devices based on OECTs show volatile and tunable dynamics suitable for the emulation of short-term synaptic plasticity functions. Chemical synthesis allows for the introduction of non-volatile phenomena suitable for long-term memory functions. The device operation in common electrolyte permits the definition of spatially distributed multiple inputs at a single device level. The presence of a global electrolyte in an array of devices also allows for the homeostatic or global control of the array. Global electrical oscillations can be used as global clocks that frequency-lock the local activity of individual devices in analogy to the global oscillations in the brain. Finally, “soft” interconnectivity through the electrolyte can be defined, a feature that paves the way for parallel interconnections between devices with minimal hard-wired connections.

Electrochromism (EC) is defined as a reversible color change by electrochemical redox reaction and has several features such as color variation, memory property and so on. Multifunctional electrochromic materials which control multiple colors, various color density, and specular reflection are expected to be potential candidate for light-modulation device such as smart window and novel reflective display device such as e-paper. This paper focuses on novel EC system toward energy-saving technology and full color e-paper, based on electrochemical reaction. Electrodeposition is an attractive method in electrochromism to create several optical states (colors) because silver (Ag) nanoparticles exhibit various optical states based on their localized surface plasmon resonance (LSPR). LSPR bands of metal nanoparticles are affected by the size and shape. The control of LSPR band, therefore, must enable dramatic changes in color for the surface where nanoparticles are deposited. We successfully demonstrate the first LSPR-based multicolor EC device enabling reversible control of six optical states such as transparent, silver mirror, cyan, magenta, yellow and black, which is attractive for smart window as well as color e-paper application. We will discuss the mechanism of electrodeposition and a wide range of its applications.

An azo dye DR1 was incorporated into DNA complex (DNA-CTMA) films as a guest dispersed in the host or as a copolymer (pDR1) side chain blended with the complex. Although the guest did not show photo-isomerization response, DR1 side chain in the blend showed photo-induced birefringence and photo-induced transparency under the excitation at 532 nm. Several cationic dyes were incorporated into pDR1/DNA-CTMA films with immersion method. Rhodamine 640 perchlorate showed amplified spontaneous emission with the excitation above 10mJ/cm² by a pulsed laser of 532 nm.

We demonstrate a new device concept for organic photodetectors to overcome the lack of organic materials efficiently absorbing in the near-infrared spectral region. We exploit the properties of the weakly absorbing charge transfer state formed at the donor-acceptor interface in a bulk hetero junction photovoltaic device implemented into a specially designed optical microcavity [1]. This enables us to spectrally selective detect light with wavelengths up to 1700 nm. Based on this technological platform, we build a miniaturized 16-channel spectrometer without the need for further optical elements such as gratings or prisms for food screening applications and liquid analysis. With very high and competitive detectivities, we are entering the Indium-Gallium-Arsenide dominated world and show a route towards low-cost applications and novel devices. [1] B. Siegmund et al. Nature Communications 8, 15421 (2017)

The individualized functionalization of mass-produced microstructures is still challenging for the process technology. Here, a rroll-to-roll based process hot embossing is presented for the production of microfluidic structures by means of hot embossing is presented. The resulting microfluidic channels are functionalized modified with different materials. Thereby, digital printing technologies such as aAerosoljet or inkjet are used. This approach allows for mass production of microfluidic channels and their the individualized individual functionalizationfunctionalization of mass produced microfluidic channels. The encapsulation of the channels also takes placeis realized in an R2R-based thermal bonding process without adding any solvent or adhesive. Taking account ofUsing this approach, several sensor systems for gas and / or fluid detection could be demonstrated. Surface -eEnhanced Raman Scattering scattering (SERS) with amplification enhancement factors of up to 107 [1] is demonstrated by printing gold nanoparticles into the microfluidic channel. We evaluate the printed SERS structures using solutions of rhodamine 6G and adenosine as exemplary analytes. Furthermore, these channels could be functionalized with different fluorescent organic semiconductors. Their fluorescence intensity is quenched in the presence of a nitroaromatic compounds. By using different materials simultaneously, we are able to measure a fingerprint like pattern of different analytes, which we evaluated by means ofusing pattern recognition algorithms. This method can be used both in the gas phase (electronic nose) and in fluids (electronic tongue) for the detection of nitroaromatic compounds [2,3]. With the opto-electronic nose, we were able to reach detections limits below 1ppb. [1] A. Habermehl et al, Sensors 17, 2401 (2017). [2] N. Bolse et al, Flexible and Printed Electronics 2, 024001 (2017) [3] N. Bolse et al, ACS Omega 2 (10), 6500-6505 (2017)

Electronic devices comprising biocompatible materials will open the pathway to a whole new field of future applications ranging from healthcare and medicine to smart packaging and disposable electronics. In this work we present the fabrication of light-emitting electrochemical cells comprising a non-halogenated bio-friendly solid-polymer electrolyte on biodegradable cellulose di-acetate substrates by industrially relevant printing techniques. By using a biocompatible electrode system consisting of PEDOT:PSS and ZnO we could produce functional devices comprising up to 99 vol% of biocompatible materials. The devices are semi-transparent and flexible even under operation. A maximum luminance of over 200 cd m-2 is achieved significant for display and lightning applications. The relatively short lifetime on the timescale of some minutes can be compensated by a fully-printed production process utilizing inkjet printing and blade coating, relevant for an industrially cost-efficient large-scale production of disposable electronics.

We present the utilization of inorganic, organic, and hybrid (perovskite) thin film photodetectors in (bio)chemical sensing where OLEDs are used as the excitation source in compact devices. The sensitivity and feasible operational mode, whether monitoring the effect of the analyte concentration on the photoluminescence intensity or decay time following an OLED pulse will be discussed. While monitoring the PL decay time is the preferred operational mode, charge trapping and other defects impede the photodetectors’ response time, limiting the analysis dynamic range. Analytes tested include oxygen, glucose, lactate, and ethanol. Examples of all organic sensors for these analytes will be presented. The use of thin film photodetectors in on-chip (integrated all-organic) spectrometers will also be shown.

Flexible sensors offer advantages such as light weight, cost effective, the potential to be manufactured with roll-to-roll equipment and to be used in portable and wearable devices. To remain as a cost-effective device, there is a need to reduce fabrication process expenses while preserving high sensitivity and responsivity. In this paper we demonstrate a novel method for facile fabrication of lead halide perovskite photosensor on a flexible substrate with high sensitivity. Capillary motion of perovskite precursor was employed as a convenient and simple technique to create a patterned layer of perovskite. Scanning electron microscope was employed to characterize fabricated perovskite layer. Fabricated layer was used in an ITO-perovskite-ITO structure to be used as a photosensor. Electrical and optical characteristics of the device have been investigated. The responsivity and the sensitivity of the device at 2.0 V were measured to be 0.1 A/W and 172, respectively. Finally, optical properties of the fabricated device were compared with another photodetector fabricated by conventional lithography process. The photocurrent of the sample, made by utilizing capillary motion, at 2.0 V was found to be 211 nA which was 2.8 times higher than the photocurrent of the sample made by traditional method (76 nA at 2.0 V). This novel method has shown great potential for commercial application.

We report on a nanoscale semiconducting optoelectronic system optimized for neuronal stimulation: the organic electrolytic photocapacitor. The devices comprise a trilayer of metal and p and n semiconductors. When illuminated in physiological solution, these metal-semiconductor devices charge up, transducing light pulses into localized displacement currents that are strong enough to stimulate cells. The devices are freestanding, requiring no wiring or external bias, and are stable in physiological conditions. We have systematically evaluated the ability of photocapacitor devices to alter the cell membrane potential of single nonexcitable cells, generate action potentials in neuronal cell cultures, and stimulate explanted light-insensitive embryonic retinas.

Organic semiconductors in different shapes and composition can be interfaced with living cells. This provides a new, exciting route towards optical control of physiological functions or the restoring of natural functions, e.g. vision. In this talk I will present a number of experiments that show the effective abiotic-biotic coupling of organic semiconductors with cells and small animals, suggesting the potential of organic light actuators for geneless opto stimulation. Investigated systems are all based on polythiophene as photoactive layer, in planar films, nanostructured layers or nanoparticles. Spectroscopy, photo-electrochemistry and photo-electrophysiology are exploited to carry out the experimental investigations. We report on photoluminescence in vivo of nanoparticles and other light actuators. While the mechanism explaining such coupling is still unknown, it is appearing that thermal, capacitive, faradaic or chemical coupling are all options to be carefully evaluated.

Electronic transport is predominantly the domain of man-made materials and devices. Biology, on the other hand, tends to manage charge conduction via transport of ions. Consequently, interfacing biological and synthetic systems is an imperfect and often crude endeavor. New materials to interface with specific cellular and enzymatic processes are required to address challenges in integrating biology with electronic systems. Nature provides inspiration for exactly such biointerface materials. Many microbes in anoxic soils and sediment respire using extracellular electron transfer. Some of these species, specifically of the Geobacter genus, synthesize fiber-like appendages, called pili, which conduct charge over distances of microns to millimeters to reach remote electron acceptors. Our studies show that the conductivity in Geobacter pili is inherent to the protein fibers themselves, and that they exhibit band-like electronic transport characteristics. Understanding how extended protein fibers can support band-like transport is impractical in Geobacter pili, in part due to the lack of an appropriate crystal structure. Based on sequence and structure motifs from native pili fibers, we instead developed a new class of self-assembling de novo peptides with well-defined solid state X-ray crystallographic structure and solution behavior. These peptides self-assemble through a novel coiled-coil interaction, a Phe-Ile zipper, to form unique, antiparallel hexamers (ACC-Hex) and fibers. The Phe-Ile zipper motif is general, allowing for the incorporation of various natural and non-natural amino acid mutations. These sequence variants were used to determine the assembly mechanism of ACC-Hex and create coiled coils with uncommonly high stability to denaturation. Fibers assembled from these peptides are electrically conductive and exhibit characteristics of band-like electronic transport, similar to Geobacter pili, making them ideal for device applications. These self-assembling peptides potentially expand the synthetic biology toolkit to include autonomously-generated bioelectronics interfaces, and their well-defined structure suggests them as an experimental platform to study structure-property relationships of long-range electronic conduction in proteins and other amino acid biomaterials.

Paper and ink have been continually evolving since their invention. Conventional printing quality and cost is constantly improving, yet only few examples of commercial embedded electronics on paper exist. This is due to the fact that inks with optical and electronic properties do not suit conventional paper and are still challenging to print reliably. In this project, we aim to develop a new generic mass media “next generation” paper. We present the challenges and progress on book augmentation, using printing technologies such as screen printing and roll-to-roll fabrication. This first step aims to create an augmented book prototype via hybrid integration of optical sensors in its pages and by embedding energyefficient control and communication electronics in the cover. The system senses user interaction and, through wireless connectivity, presents the user with relevant, updated digital content on an adjunct device. The proposed fabrication sequence has been developed with close attention to the requirements of industrial scale-up.

A Printed pressure sensor is demonstrated to measure dynamic pressure of the blood flow in an artificial blood vessel construct. The sensor is an oscillator with printed inductor and compressible porous PDMS capacitor which responds to the changing pressure. The variable capacitance of capacitor modulates the resonance frequency of the LC oscillator. Outside the vessel a readout coil connected to a network analyzer measures the resonance frequency of the LC oscillator, which changes with the applied pressure in the liquid environment. The inductor coils in the sensor circuit and outer readout coil are optimized for higher wireless response by increasing the trace conductivity and geometric designs. Also the porous PDMS capacitor is tuned by pore size and concentration to increase the reliability and sensitivity under changing pressure. The sensor responded to dynamic liquid pressure in the range of 30~170 mmHg within 50 msec, and the current measurement setup followed pulse frequency up to 144 beats per minute. The application of this sensor can be extended to monitoring fluid pressure in other structures, such as in microfluidic chips and environmental monitoring devices.

Organic diode rectifier have attracted a lot of attention recently for RF energy harvesting, and much effort has been applied toward extending the ultra-high frequency range [1-2]. An important parameter that should be considered for diodes used in RF rectifier is the turn on voltage, which should be low to overcome the problem of the low voltage generated and power extracted from energy harvesting. In this work, we focused on pentacene organic rectifier with high rectification ratio and low threshold voltage obtained by tuning the work function of gold with a self-assembled monolayer of PFBT and optimizing the thickness of the organic layer. We demonstrate a high rectification ratio up to 107 and a very low turn on voltage as low as 20 mV. Flexible rectifier diode have been also fabricated in release paper WO84, high rectification ratio of 106 was obtained even after bending of the device. The pentacene based rectifier diodes were also demonstrated to operate at more than 1GHz. This provides a great potential for fabricating high-performance organic flexible diodes and opens the way for the development of high frequency response using organic materials. References [1] D. Im et al, adv. Mater. 23, 644-648 (2011). [2] C-mo. Kang et al, adv. Electron. Mater. 2, 1500282 (2016).

The resistive switching mechanism in organic and hybrid resistive memories has been intensively studied in the last years. A particular interest have been directed to solution processed resistive layers based on an organic or polymer compounds for which convincing direct and indirect evidences indicated that the switching mechanism is based on the formation of conductive filaments (CFs) bridging the two metal electrodes. However, the CF composition, formation and rupture dynamics and evolution during the prolonged cycling are still poorly explored. Experiments are rare because of the well-known challenges in characterizing nanoscale filaments. In this work, we combine time-of-flight secondary ion mass spectrometry (ToF-SIMS) 3D imaging and in-situ atomic force microscopy (AFM), acquired at different profile depths, to characterize the CF composition and dynamics in high-performance and environmental stable crossbar Ag/parylene C/Ag printed memories. The results allow characterizing the filaments composition, their formation mechanism by electrochemical metallization and their evolution upon cycling. Moreover, the AFM images allow for a more clear interpretation of ToF-SIMS 3D reconstructions of molecular ions and to highlight artifacts arising from the different sputtering rate of metals as compared to the organic material.

Organic-based electrochemical metallization memory (ECM) has been paid much attention for non-volatile memory devices owing to high integration and mechanical flexibility. In such ECM systems, the formation of conductive filaments (CFs) is typically composed of two activation steps: i) the electrochemical redox reactions at an interface between an electrode and an electrolyte and ii) the migration of the cations of metal across the electrolyte. Accordingly, the overall electrical performance of the ECM device is primarily governed by the kinetics of the two steps. However, in the ECM devices using organic electrolytes, a rather compete picture of the resistive switching during the ion-migration process has not been described so far since filamentary paths are barely observable. In this work, we investigated how the resistive switching depends on the ion-migration properties including the drift velocity and the migration path in the organic ECM device. Two types of polymer electrolytes, having different molecular weights, were used for the control of the ion drift velocity. The topography of ion-migration paths was modified by the deposition rate of metal for the top electrode. The formation and the retention of the CFs depend critically on the ion mobility of the polymer electrolyte and the topography of the ion-migration paths as well. These results will provide a useful guideline for constructing high- performance ECM storage systems based on organic materials. This work was supported by the Brain Korea 21 Plus Project in 2018.

Electrolyte-gated organic field-effect transistors (EGOFETs) are the transducer of choice for many ion- and biosensor applications. Due to the formation of an electric double layer at the electrolyte/organic semiconductor interface, they exhibit a very high capacitance allowing for low-voltage and therefore the necessary stable operation in aqueous environment. We show that also using poly(3-hexylthiophene) (P3HT) based EGOFET devices, one can overcome oxygen and water induced degradation processes, normally observed for this polymer, when operating the device in the right gate potential window, avoiding electrochemical processes at the polymer water interface. Moreover, the use of a polymeric blend of P3HT with poly(methyl methacrylate) (PMMA) as the active layers showed improve device stability, as it was tested. We also tested the response of the device as function of the distance between the active EGOFET and the gate wire, aiming to use the device in different sensor applications. Based on the transfer curves of the devices, it was found that the choice of a proper operational window is the most critical parameter and seems to limit both P3HT and P3HT:PMMA systems to the same gate potential which seem to be more important than choice of the semiconductor material as such. Moreover, we could show that the EGOFET device performance is almost independent of the distance between the gate wire and the device pixel within the correct gate potential window.

Standard models for evaluating the electro-optic (EO) response of organic materials typically assume that the refractive index of the material in the absence of a RF modulation field is isotropic and homogeneous. Such assumptions work very well for low-concentration guest-host materials in bulk devices. However, current generation organic EO materials at high densities and under nanoscale confinement can show sufficient birefringence to affect device performance. We use computer simulations and spectroscopic experiments to characterize and predict changes in the index of refraction under poling. We also demonstrate that poling-induced birefringence can lead to a non-linear relationship between the apparent EO coefficient and poling field strength.

We review the development of molecular, exogenic probes for the application of nonlinear optical imaging. The emphasis necessarily is on requirements for second-harmonic imaging, because of the more stringent noncentrosymmetry requirements imposed at both the molecular and the structural level. We focus on the application in cellular imaging, where the challenge is the specificity. Because of the serendipitous use of charges on the probes for the optimization of both the amphiphilic and the optical properties, we recall how hyper-Rayleigh scattering has been instrumental in this development. This also holds true for the fluorescent proteins and examples of fluorescent and chromoproteins for nonlinear imaging will be presented.

The multifunctional flexible nanocomposite films were developed and characterized. To improve the sensitivity, the novel P(VDF-TrFE) film-sensors embedded with carbon nano-particles were synthesized and fabricated via the solution casting technique. The fabricated films were characterized for dielectric, piezoresistive, and pyroelectric properties so as to predict performance of the sensors for pressure, thermal detection, and energy harvesting. The results obtained are presented and discussed.

Polymeric conjugated materials and composites are very promising for developing future soft material semiconductor and conductor based devices due to their inherent advantages such as lightweight, flexible shape, low-cost, ease of processability, ease of scalability, biocompatibility, etc. Like inorganic semiconductors, the addition of certain minority molecules or dopants can significantly alter the electronic structures and properties of the host conjugated polymers or composites allowing tunablilty for a variety potential applications including, but may not limited to, electronic devices (e.g., field effect transistors and related sensors), optoelectronic devices (e.g., photo sensors, solar cells), thermoelectric devices (e.g., temperature sensors, thermoelectric generators), etc. In this work, P3HT and P3HT:PCBM doped with various iodine doping levels were systematically evaluated on morphology, electronic property, and potential multi-function or sensor applications. This study finds that an optimal ratio of iodine doping resulting in a smallest inter-layer gap of the P3HT edge-on main chain packing style. This result may account for an optimal electronic/optoelectronic performance of an iodine doped P3HT/PCBM photoelectric device. Most importantly, the iodine/P3HT/PCBM ternary composite materials exhibit photoelectric and thermoelectric dual conversions simultaneously, and that one input can modulate the other conversion or function. The results and findings of this study could be very useful to understand and to guide the design and development of future generation high efficiency molecular or polymer based multifunction sensory or modulation devices.

The effect of laser irradiation is one of the most important factors that affect the bacteria survival due to the wavelengths that emit the different light sources. The high-intensity broadband visible light (400–800nm) can reduce viability of bacterial strains. The main objective is to assess the most effective wavelengths of visible light in growth of four beneficial rhizobacteria. The survival of bacterial cells following illumination was monitored by optical density after exposure of the suspended bacteria to light at different time of incubation. Bacterial grow under the same conditions but without light exposure as controls. The visible light with wavelength between 450-590nm increase the bacterial growth in vitro conditions.