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A Point-of-Care system for molecular diagnosis (PoC-MD) is described, combining GaN and CMOS chips. The device is a micro-system for fluorescence measurements, capable of analyzing both intensity and lifetime. It consists of a hybrid micro-structure based on a 32 × 32 matrix addressable GaN microLED array, with square LEDs of 50 µm edge length and 100 µm pitch, with an underneath wire bonded custom chip integrating their drivers and placed face-to-face to an array of 16 × 16 single-photon avalanche diodes (SPADs) CMOS. This approach replaces instrumentation based on lasers, bulky optical components, and discrete electronics with a full hybrid micro-system, enabling measurements on 32 × 32 spots. The reported system is suitable for long lifetime (>10 ns) fluorophores with a limit of detection ~1/4 µM. Proof-of-concept measurements of streptavidin conjugate Qdot™ 605 and Amino PEG Qdot™ 705 are demonstrated, along with the device ability to detect both fluorophores in the same measurement.

Color QR Codes are often generated to encode digital information, but one also could use colors or to allocate colors in a QR Code to act as a color calibration chart. In this dataset, we present several thousand QR Codes images generated with two different colorization algorithms (random and back-compatible) and several tuning variables in these color encoding. The QR Codes were also exposed to three different channel conditions (empty, augmentation and real-life). Also, we derive the SNR and BER computations for these QR Code in comparison with their black and white versions. Finally, we also show if ZBar, a commercial QR Code scanner, is able to read them.

Abstract Performing long-term cell observations is a non-trivial task for conventional optical microscopy, since it is usually not compatible with environments of an incubator and its temperature and humidity requirements. Lensless holographic microscopy, being entirely based on semiconductor chips without lenses and without any moving parts, has proven to be a very interesting alternative to conventional microscopy. Here, we report on the integration of a computational parfocal feature, which operates based on wave propagation distribution analysis, to perform a fast autofocusing process. This unique non-mechanical focusing approach was implemented to keep the imaged object staying in-focus during continuous long-term and real-time recordings. A light-emitting diode (LED) combined with pinhole setup was used to realize a point light source, leading to a resolution down to 2.76 μm. Our approach delivers not only in-focus sharp images of dynamic cells, but also three-dimensional (3D) information on their (x, y, z)-positions. System reliability tests were conducted inside a sealed incubator to monitor cultures of three different biological living cells (i.e., MIN6, neuroblastoma (SH-SY5Y), and Prorocentrum minimum). Altogether, this autofocusing framework enables new opportunities for highly integrated microscopic imaging and dynamic tracking of moving objects in harsh environments with large sample areas.

MicroLED arrays with the capability of switching each pixel separately with high frequency can serve as structured micro-illumination light engines for applications in sensing, optogenetics, microscopy and many others. We describe a scalable chip process chain for the fabrication of passive-matrix microLED arrays, which were integrated with PCB-based driving electronics. The arrays were produced by deep-etching of conventional planar LED structures on sapphire, followed by filling and planarization steps. The pixel resolution lies in the range of 254 to 2540 pixels-per-inch (ppi), the arrays consist of 32 x 32 pixels. Optical output powers up to 50 µW per pixel were measured. In comparison to CMOS-based approaches, the presented technology is a simplified strategy to produce microLED arrays with high pixel counts.

Though integrating functional organic materials with semiconductor nanostructures is attractive for 3D chip processing, realizing these hybrids remains a challenge. Here, the authors report an oxidative chemical vapor deposition-based process for designing novel 3D hybrid optoelectronic structures.

Abstract Background In this work, a nanostructured guided-mode resonance filter matrix with high transmission efficiency and narrow bandwidth is demonstrated. The developed nano-filter arrays have various usages, e.g., combined with the CMOS image sensors to realize compact spectrometers for biomedical sensing applications. Methods In order to optimize the filter performance, the spectral responses of filters with different structural parameters are carefully studied based on the variable-controlling method. A quality factor is carried out for quantitative characterization. Results In this case, a high fill factor of 0.9 can strongly suppress sidebands, while buffer layer thickness can be adjusted to mainly control the bandwidth. The transmission peaks shift from 386 nm to 1060 nm with good linearity when periods vary from 220 nm to 720 nm. The incident angle dependence is simulated to be ~ 1.1 nm/degree in ±30° range. The filters are then fabricated and characterized. The results obtained from both simulations and experiments agree well, where the filters with the period of 352 nm exhibit simulated and measured transmission peaks of 564 nm and 536 nm, the FWHM of 13 nm and 17 nm, respectively. In terms of metal material, besides aluminum, silver is also investigated towards optimization of the transmission efficiency. Conclusion The transmission spectra of designed filters have high transmission and low sideband; its peaks cover the whole visible and near infrared range. These characteristics allow them to have the possibility to be integrated into image sensors for spectrometer applications.

Abstract This paper reports on the direct qualitative and quantitative performance comparisons of the field-effect transistors (FETs) based on vertical gallium nitride nanowires (GaN NWs) with different NW numbers (i.e., 1–100) and diameters (i.e., 220–640 nm) fabricated on the same wafer substrate to prove the feasibility of employing the vertical 3D architecture concept towards massively parallel electronic integration, particularly for logic circuitry and metrological applications. A top-down approach combining both inductively coupled plasma dry reactive ion etching (ICP-DRIE) and wet chemical etching is applied in the realization of vertically aligned GaN NWs on metalorganic vapor-phase epitaxy (MOVPE)-based GaN thin films with specific doping profiles. The FETs are fabricated involving a stack of n-p-n GaN layers with embedded inverted p-channel, top drain bridging contact, and wrap-around gating technology. From the electrical characterization of the integrated NWs, a threshold voltage (V th) of (6.6 ± 0.3) V is obtained, which is sufficient for safely operating these devices in an enhancement mode (E-mode). Aluminium oxide (Al2O3) grown by atomic layer deposition (ALD) is used as the gate dielectric material resulting in nearly-zero gate hysteresis (i.e., forward and backward sweep V th shift (ΔV th) of ~0.2 V). Regardless of the required device processing optimization for having better linearity profile, the upscaling capability of the devices from single NW to NW array in terms of the produced currents could already be demonstrated. Thus, the presented concept is expected to bridge the nanoworld into the macroscopic world, and subsequently paves the way to the realization of innovative large-scale vertical GaN nanoelectronics.

We present the combined analysis of electroluminescence (EL) and current–voltage (I–V) behavior of single, freestanding (In,Ga)N/GaN nanowire (NW) light-emitting diodes (LEDs) in an unprocessed, self-assembled ensemble grown by molecular beam epitaxy. The data were acquired in a scanning electron microscope equipped with a micromanipulator and a luminescence detection system. Single NW spectra consist of emission lines originating from different quantum wells, and the width of the spectra increases with decreasing peak emission energy. The corresponding I–V characteristics are described well by a modified Shockley equation. The key advantage of this measurement approach is the possibility to correlate the EL intensity of a single-NW LED with the actual current density in this NW. This way, the external quantum efficiency (EQE) can be investigated as a function of the current in a single-NW LED. The comparison of the EQE characteristic of single NWs and the ensemble device allows for a quite accurate determination of the actual number of emitting NWs in the working ensemble LED and the respective current densities in its individual NWs. This information is decisive for a meaningful and comprehensive characterization of a NW ensemble device, rendering the measurement approach employed here a very powerful analysis tool.

The three-dimensionality of 3D GaN field-effect transistors (FETs) provides them with unique advantages compared to their planar counterparts, introducing a promising path towards future FETs beyond Moore's law. Similar to today's Si processor technology, 3D GaN FETs offer multi-gate structures that provide excellent electrostatic control over the channel and enable very low subthreshold swing values close to the theoretical limit. Various concepts have been demonstrated, including both lateral and vertical devices with GaN nanowire (NW) or nanofin (NF) geometries. Outstanding transport properties were achieved with laterally contacted NWs that were grown in a bottom-up approach and transferred onto an insulating substrate. For higher power application, vertical FETs based on regular arrays of GaN nanostructures are particularly promising due to their parallel integration capability and large sidewall surfaces, which can be utilized as channel area. In this paper, we review the current status of 3D GaN FETs and discuss their concepts, fabrication techniques, and performances. In addition to the potential benefits, reliability issues and difficulties that may arise in complex 3D processing are discussed, which need to be tackled to pave the way for future switching applications. Keywords: GaN, 3D architecture, Nanowire, Nanofin, Nanoelectronics, Field-effect transistor (FET), Vertical transistor, Lateral transistor

In this work, nitrogen dioxide (NO2) gas sensors based on zinc oxide nanorods (ZnO NRs) decorated with gold nanoparticles (Au NPs) working under visible-light illumination with different wavelengths at room temperature are presented. The contribution of localized surface plasmon resonant (LSPR) by Au NPs attached to the ZnO NRs is demonstrated. According to our results, the presence of LSPR not only extends the functionality of ZnO NRs towards longer wavelengths (green light) but also increases the response at shorter wavelengths (blue light) by providing new inter-band gap energetic states. Finally, the sensing mechanism based on LSPR Au NPs is proposed.

The recent advances in chip-size microscopy based on optical scanning with spatially resolved nano-illumination light sources are presented. This new straightforward technique takes advantage of the currently achieved miniaturization of LEDs in fully addressable arrays. These nano-LEDs are used to scan the sample with a resolution comparable to the LED sizes, giving rise to chip-sized scanning optical microscopes without mechanical parts or optical accessories. The operation principle and the potential of this new kind of microscope are analyzed through three different implementations of decreasing LED dimensions from 20 µm down to 200 nm.

Recent research into miniaturized illumination sources has prompted the development of alternative microscopy techniques. Although they are still being explored, emerging nano-light-emitting-diode (nano-LED) technologies show promise in approaching the optical resolution limit in a more feasible manner. This work presents the exploration of their capabilities with two different prototypes. In the first version, a resolution of less than 1 µm was shown thanks to a prototype based on an optically downscaled LED using an LED scanning transmission optical microscopy (STOM) technique. This research demonstrates how this technique can be used to improve STOM images by oversampling the acquisition. The second STOM-based microscope was fabricated with a 200 nm GaN LED. This demonstrates the possibilities for the miniaturization of on-chip-based microscopes.

Abstract Recently, colored H-doped TiO2 (H-TiO2) has demonstrated enhanced photoelectrochemical (PEC) performance due to its unique crystalline core—disordered shell nanostructures and consequent enhanced conduction behaviors between the core-shell homo-interfaces. Although various hydrogenation approaches to obtain H-TiO2 have been developed, such as high temperature hydrogen furnace tube annealing, high pressure hydrogen annealing, hydrogen-plasma assisted reaction, aluminum reduction and electrochemical reduction etc., there is still a lack of a hydrogenation approach in a controlled manner where all processing parameters (temperature, time and hydrogen flux) were precisely controlled in order to improve the PEC performance of H-TiO2 and understand the physical insight of enhanced PEC performance. Here, we report for the first time a controlled and local rapid thermal annealing (RTA) approach to prepare hydrogenated core-shell H-TiO2 nanorods grown on F:SnO2 (FTO) substrate in order to address the degradation issue of FTO in the typical TiO2 nanorods/FTO system observed in the conventional non-RTA treated approaches. Without the FTO degradation in the RTA approach, we systematically studied the intrinsic relationship between the annealing temperature, structural, optical, and photoelectrochemical properties in order to understand the role of the disordered shell on the improved photoelectrochemical behavior of H-TiO2 nanorods. Our investigation shows that the improvement of PEC performance could be attributed to (i) band gap narrowing from 3.0 to 2.9 eV; (ii) improved optical absorption in the visible range induced by the three-dimensional (3D) morphology and rough surface of the disordered shell; (iii) increased proper donor density; (iv) enhanced electron–hole separation and injection efficiency due to the formation of disordered shell after hydrogenation. The RTA approach developed here can be used as a suitable hydrogenation process for TiO2 nanorods/FTO system for important applications such as photocatalysis, hydrogen generation from water splitting and solar energy conversion.

Besides high-power light-emitting diodes (LEDs) with dimensions in the range of mm, micro-LEDs (μLEDs) are increasingly gaining interest today, motivated by the future applications of μLEDs in augmented reality displays or for nanometrology and sensor technology. A key aspect of this miniaturization is the influence of the structure size on the electrical and optical properties of μLEDs. Thus, in this article, investigations of the size dependence of the electro-optical properties of μLEDs, with diameters in the range of 20 to 0.65 μm, by current–voltage and electroluminescence measurements are described. The measurements indicated that with decreasing size leakage currents in the forward direction decrease. To take advantage of these benefits, the surface has to be treated properly, as otherwise sidewall damages induced by dry etching will impair the optical properties. A possible countermeasure is surface treatment with a potassium hydroxide based solution that can reduce such defects.

The combination of optics and microfluidics for particle detection makes it possible to fabricate small low-cost devices. In such hybrid-on-chip systems with integrated µLEDs, the particles can be close to the light source, which is beneficial for the detection capability according to the simulation results. In addition, further advantages and extension possibilities of such devices are discussed.

In this work, we present conductometric gas sensors based on p-type calcium iron oxide (CaFe2O4) nanoparticles. CaFe2O4 is a metal oxide (MOx) with a bandgap around 1.9 eV making it a suitable candidate for visible light-activated gas sensors. Our gas sensors were tested under a reducing gas (i.e., ethanol) by illuminating them with different light-emitting diode (LED) wavelengths (i.e., 465−640 nm). Regardless of their inferior response compared to the thermally activated counterparts, the developed sensors have shown their ability to detect ethanol down to 100 ppm in a reversible way and solely with the energy provided by an LED. The highest response was reached using a blue LED (465 nm) activation. Despite some responses found even in dark conditions, it was demonstrated that upon illumination the recovery after the ethanol exposure was improved, showing that the energy provided by the LEDs is sufficient to activate the desorption process between the ethanol and the CaFe2O4 surface.

In this contribution we present a highly miniaturized device that integrates a photoactive material with a highly efficient LED light source. This so-called micro light plate configuration (µLP) allows for maximizing the irradiance impinging on the photoactive material, with a minimum power consumption, excellent uniformity and accurate control of the illumination. We demonstrate that, with the µLP approach, very efficient low power gas sensors can be built, and provide a detailed analysis of the rationales behind such improvement, as well as a quantitative model and a set of design rules to implement it in further integrated applications. As a demonstrator, we will describe a NO2 gas sensor operating in the part per billion range (ppb) with microwatt (µW) power consumption. These are the best figures reported to date in conductometric metal-oxides (MOX) sensors operated with light (instead of heat) at room temperature.

Continuous cell culture monitoring as a way of investigating growth, proliferation, and kinetics of biological experiments is in high demand. However, commercially available solutions are typically expensive and large in size. Digital inline-holographic microscopes (DIHM) can provide a cost-effective alternative to conventional microscopes, bridging the gap towards live-cell culture imaging. In this work, a DIHM is built from inexpensive components and applied to different cell cultures. The images are reconstructed by computational methods and the data are analyzed with particle detection and tracking methods. Counting of cells as well as movement tracking of living cells is demonstrated, showing the feasibility of using a field-portable DIHM for basic cell culture investigation and bringing about the potential to deeply understand cell motility.

UV-light emitting diodes (395–278 nm) were used to investigate the gas sensing attributes of planar and nanostructured ZnO/AlN thin films on Si substrate towards NO2 at room temperature. A significant increased sensitivity ((Rg − Ra)/Ra = 65.3 ppm NO2 in air) and a strong reduction in recovery time (Trec = 14 min) were already observed for the planar ZnO/AlN thin films under UV-B (305 nm) irradiation compared to the other UV wavelengths, while the device showed no obvious response in dark. By enlarging the surface-to-volume ratio of the sensors (i.e., creating nanostructured ZnO/AlN thin films), an increased response time is expected to be observed.

A silicon photonic microresonator comprising two curved vertical grating couplers and a single suspended Si nanowaveguide (NWG) is developed to investigate the giant enhanced Brillouin scattering in subwavelength NWGs caused by photon-phonon interaction. Finite element modelling based on COMSOL Multiphysics is conducted to optimize the critical device parameters (e.g., waveguide width, height, and length). As the smallest structures that need to be resolved are down to ~15 nm in size, electron-beam nanolithography is employed. In this case, dosage tests are carried out to minimize proximity charging effects during the nanopatterning of the silicon-on-insulator (SOI) surface, resulting in appropriate adaptive current area dosage distributions for the periodic gratings, couplers peripheral areas, and NWG, respectively. Furthermore, an enhanced inductively coupled plasma dry reactive ion etching (ICP-DRIE) process at a cryogenic temperature is used to realize smooth vertical sidewalls. Finally, buffered hydrofluoric acid (BHF)-based wet chemical etching is carried out to remove the buried oxide resulting in a suspended Si waveguide.

Guidelines for the fabrication of nanoscale light-emitting diode arrays (i.e., nanoLED arrays) based on patterned gallium nitride (GaN) with very small dimensions and pitches have been derived in this work. Several challenges during top-down LED array processing have been tackled involving hybrid etching and polymer-based planarization to yield completely insulated highaspect-ratio LED fin structures and support the creation of p-GaN crossing line contacts, respectively. Furthermore, simulations of the light emission patterns were also performed providing hints for enhancing the device designs. As a result, regardless of the required device processing optimization, the developed nanoLED arrays are expected to offer high potential as novel illumination sources in biomedical imaging and sensing applications (e.g., mini compact microscopes and wearable biological/chemical nanoparticle counters)

Gas sensors based on CaFe2O4 nanopowders, which are p⁻type metal oxide semiconductor (MOX), have been fabricated and assessed for ethanol gas monitoring under visible light activation at room temperature. Regardless of their inferior sensitivity compared to thermally activated counterparts, the developed sensors have shown responsive sensing behavior towards ethanol vapors confirming the ability of using visible light for sensor activation. LEDs with different wavelengths (i.e., 465⁻590 nm) were employed. The highest sensitivity (3.7%) was reached using green LED activation that corresponds to the band gap of CaFe2O4.

A compact lensless microscope comprising a custom-made LED engine and a CMOS imaging sensor has been developed for live-cell culture imaging inside a cell incubator environment. The imaging technique is based on digital inline-holographic microscopy, while the image reconstruction is carried out by angular spectrum approach with a custom written software. The system was tested with various biological samples including immortalized mouse astrocyte cells inside a petri dish. Besides the imaging possibility, the capability of automated cell counting and tracking could be demonstrated. By using image sensors capable of video frame rate, time series of cell movement can be captured.

Arrays of 1D-vertically arranged gallium nitride (GaN) nanorods (NRs) are fabricated on sapphire and connected to both bottom and freestanding top contacts. This shows a fully validated top-down method to obtain ordered arrays of high-surface-to-volume elements that can be electrically interrogated and used, e.g., for sensing applications. Specifically, these will be used as highly integrated heating elements for conductometric gas sensors in self-heating operation. Detailed fabrication and processing steps involving inductively coupled plasma reactive ion etching (ICP-RIE), KOH-etching, interspace filling, and electron-beam physical vapor deposition technologies are discussed, in which they can be well adjusted and combined to obtain vertical GaN NRs as thin as 300 nm in arbitrarily large and regular arrays (e.g., 1 × 1, 3 × 3, 9 × 10 elements). These developed devices are proposed as a novel sensor platform for temperature-activated measurements that can be produced at a large scale offering low-power, and very stable temperature control.

Pinhole‐shaped light‐emitting diode (LED) arrays with dimension ranging from 100 μm down to 5 μm have been developed as point illumination sources. The proposed microLED arrays, which are based on gallium nitride (GaN) technology and emitting in the blue spectral region (λ = 465 nm), are integrated into a compact lensless holographic microscope for a non‐invasive, label‐free cell sensing and imaging. From the experimental results using single pinhole LEDs having a diameter of 90 μm, the reconstructed images display better resolution and enhanced image quality compared to those captured using a commercial surface‐mount device (SMD)‐based LED.

A laser lift-off (LLO) process has been developed for detaching thin InGaN/GaN lightemitting diodes (LED) from their original sapphire substrates by applying an ultrafast laser. LLO is usually based on intense UV irradiation, which is transmitted through the sapphire substrate and subsequently absorbed at the interface to the epitaxially grown GaN stack. Here, we present a successful implementation of a two-step LLO process with 350 fs short pulses in the green spectral range (520 nm) based on a two-photon absorption mechanism. Cathodo- and electroluminescence experiments have proven the functionality of the LLO-based chips. The impact of radiation on the material quality was analysed with scanning (SEM) and transmission electron microscopy (TEM), revealing structural modifications inside the GaN layer in some cases.

Transferable substrate-less InGaN/GaN light-emitting diode (LED) chips have successfully been fabricated in a laser lift-off (LLO) process employing high power ultrashort laser pulses with a wavelength of 520 nm. The irradiation of the sample was conducted in two sequential steps involving high and low pulse energies from the backside of the sapphire substrate, which led to self-detachment of the GaN stack layer without any additional tape release procedure. To guarantee their optoelectrical function and surface quality, the lifted LED chips were assessed in scanning electron microscopy (SEM) and electroluminescence (EL) measurements. Moreover, surface characterizations were done using atomic force microscopy (AFM) and Auger Electron Spectroscopy (AES).

ZnO nanorods (NRs) arrays with good vertical alignment were selectively grown on microscale patterned surfaces by a MEMS-compatible, low-temperature chemical-bath deposition method (CBD). The direct-current (DC) sputtered and subsequently annealed ZnO seed-layer was found to have a crucial effect on the ZnO NRs growth. Depending on the pre-annealing temperature between 200 °C and 700 °C, which is compatible with our microcantilever fabrication process, diameters and area densities of the NRs of 60–99 nm and 17–27 µm−2 were observed, respectively, with the best alignment at 600 °C. A surface-area enlargement factor of 48 was achieved with respect to a ZnO layer indicating the potential of ZnO NRs arrays for MEMS applications, such as gas sensing.

We developed an integrated platform to build up conductometric sensors with controlled illumination. Our device contains a miniaturized indium gallium nitride (InGaN) LED as a light source, and a set of interdigitated electrodes (IDEs) in close contact with the LED. The sensor material is later deposited on top of the IDE, to monitor its resistance. In this configuration, all the light emitted by the LED is collected by the sensor material, leading to a very efficient photoexcitation. We demonstrate the effectiveness of the approach building a photoactivated gas sensor based on ZnO operating with as little as 100 μW.

Cell registration by artificial neural networks (ANNs) in combination with principal component analysis (PCA) has been demonstrated for cell images acquired by light emitting diode (LED)-based compact holographic microscopy. In this approach, principal component analysis was used to find the feature values from cells and background, which would be subsequently employed as neural inputs into the artificial neural networks. Image datasets were acquired from multiple cell cultures using a lensless microscope, where the reference data was generated by a manually analyzed recording. To evaluate the developed automatic cell counter, the trained system was assessed on different data sets to detect immortalized mouse astrocytes, exhibiting a detection accuracy of ~81% compared with manual analysis. The results show that the feature values from principal component analysis and feature learning by artificial neural networks are able to provide an automatic approach on the cell detection and registration in lensless holographic imaging.

We present a simple an inexpensive method to implement a Griess-Saltzman-type reaction that combines the advantages of the liquid phase method (high specificity, fast response time) with the benefits of a solid implementation (easy to handle). We demonstrate that the measurements can be carried out using conventional RGB sensors; circumventing all the limitations around the measurement of the samples with spectrometers. We also present a method to optimize the measurement protocol and target a specific range of NO2 concentrations. We demonstrate that it is possible to measure the concentration of NO2 from 50 ppb to 300 ppm with high specificity and without modifying the sensing elements.

Vertically aligned 3D gallium nitride (GaN) nanowire arrays with sub-50 nm feature sizes were fabricated using a nanosphere lift-off lithography (NSLL) technique combined with hybrid top-down etching steps (i.e., inductively coupled plasma dry reactive ion etching (ICP-DRIE) and wet chemical etching). Owing to the well-controlled chemical surface treatment prior to the nanobead deposition and etching process, vertical GaN nanowire arrays with diameter of ~35 nm, pitch of ~350 nm, and aspect ratio of >10 could be realized using 500 nm polystyrene nanobead (PN) masks. This work has demonstrated a feasibility of using NSLL as an alternative for other sophisticated but expensive nanolithography methods to manufacture low-cost but highly ordered 3D GaN nanostructures.

A portable lensless imaging device combining light-emitting diodes (LEDs) and a CMOS image sensor was developed and its suitability for non-invasive live-cell in vitro monitoring of pancreatic islets was demonstrated. A microfluidic lab-on-a-chip platform containing micro wells with various depths was also fabricated and integrated into the optical sensor system, which allows for immobilization of the single islets and continuous recording of their behavior. This promising technique may provide further insight into the structure and function of pancreatic islets and their deficiencies in type 2 diabetes.

An integrated nano-optoelectronic biological sensor system is developed to obtain insights of the biochemical and physical processes of Geobacter sulfurreducens-based biofilm growth inside a miniaturized microbial fuel cell (MFC) reactor. Gallium nitride (GaN), which was used as a novel electrode material, has been investigated in terms of its biocompatibility and performance to transport the electrons delivered by the microorganisms. Moreover, in order to enhance the produced current density, vertical 3D GaN nanoarchitectures (i.e., arrays of nanowires and nanofins) with larger surface-to-volume ratios were fabricated using a top-down nanomachining method involving nanolithography and hybrid etching technique.