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Banana fruits consumption generates about 35% weight of peel waste containing approximately 10.61 to 24 w/w% of pectin. Hence, improper banana peel waste management may induce various environmental and health issues. The objectives of this work were to study the effect of substrate concentration, pH, temperature, and duration on the yield of pectin extracted from enzymatic hydrolysis of banana peel powder. In this work, the crude enzymes were obtained via submerged fermentation of Kepok Kuning banana peel powder utilising Aspergillus niger and directly used without prior purification. Pectin extraction from banana peel powder was performed through hydrolysis using crude pectinases at various substrate concentrations (0.033 to 0.123 g/mL), pH (4.0 to 6.0), and temperature (40 to 70°C) for 180 min. The increase of extraction parameters enhanced the pectin yield to a maximum value and then declined. High substrate concentration, temperature, pH, and monomeric pectin compounds formation at long hydrolysis duration were found to reduce enzyme activity. A recommended extraction condition is using 0.103 g/mL substrate concentration, pH 5.0, and 55 °C for 120 min to achieve 10.80% weight yield. Commercial implementations of the results can be worthwhile in solving the environmental problem and enhance the economic value of pectin-rich fruit peels and other agricultural wastes.

The integration of gallium nitride (GaN) nanowire light-emitting diodes (nanoLEDs) on flexible substrates offers opportunities for applications beyond rigid solid-state lighting (e.g., for wearable optoelectronics and bendable inorganic displays). Here, we report on a fast physical transfer route based on femtosecond laser lift-off (fs-LLO) to realize wafer-scale top–down GaN nanoLED arrays on unconventional platforms. Combined with photolithography and hybrid etching processes, we successfully transferred GaN blue nanoLEDs from a full two-inch sapphire substrate onto a flexible copper (Cu) foil with a high nanowire density (~107 wires/cm2), transfer yield (~99.5%), and reproducibility. Various nanoanalytical measurements were conducted to evaluate the performance and limitations of the fs-LLO technique as well as to gain insights into physical material properties such as strain relaxation and assess the maturity of the transfer process. This work could enable the easy recycling of native growth substrates and inspire the development of large-scale hybrid GaN nanowire optoelectronic devices by solely employing standard epitaxial LED wafers (i.e., customized LED wafers with additional embedded sacrificial materials and a complicated growth process are not required).

For various lighting and monolithic sensor systems application, vertically aligned three-dimensional (3D) gallium nitride (GaN)- and indium gallium nitride (InGaN)/GaN-based LED nanowire arrays with sub-200 nm feature sizes (down to 35 nm) were fabricated using a nanosphere lift-off lithography (NSLL) technique combined with hybrid top-down etching (i.e., inductively coupled plasma dry reactive ion etching (ICP-DRIE) and wet chemical etching). Owing to the lithographic opening and well-controlled surface functionalization prior to the polystyrene nanosphere (PN) deposition, vertical GaN nanowire arrays with an area density of 9.74 × 108 cm–2 and an aspect ratio of >10 could be realized in a specified large area of 1.5 × 1.5 mm2. Optoelectrical characteristics of the nanoLEDs were further investigated in cathodoluminescence (CL) measurements, in which multiquantum well (MQW) shows a clear CL-emission at a wavelength of 465 nm. Thus, using NSLL to manufacture low-cost but highly ordered 3D GaN-based nanowir...

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.

This paper reports on the fabrication of 3D silicon nanopillars (NPLs) modified with ZnO nanorods (NRs) (i.e., ZnO-NRs@Si-NPLs) on a piezoresistive Si microcantilever (MC) for sensing application. A monolayer-colloidal-crystal film of polystyrene (PS) nanoparticles (NPs) was deposited and used as physical mask for cryogenic Si dry etching. Vertically aligned Si-NPLs were selectively etched on the MC backside-surface. In addition, ZnO-NRs were grown in-situ on the Si NPLs using a sputtering/oxidizing and chemical bath deposition two-step method, resulting in a 3D ZnO-NRs@Si-NPLs on the MC backside.

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.

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.

Gallium nitride (GaN) is a promising semiconductor material for creating versatile LED devices in various applications, including solid-state lighting, augmented reality, and sensors. By transferring the nanostructured GaN LEDs onto flexible substrates, they could even exhibit enhanced performance compared to flexible organic LEDs in terms of their flexibility, longevity, and external quantum efficiency. To release GaN LED chips from their original sapphire substrates to other substrates, laser lift-off (LLO) has been regularly utilized in production of power LEDs as a reliable and reproducible technology. For the normal LLO process, photons with energies above the band gap of GaN are used, so that the energy is dissipated at the sapphire/GaN interface. These LLO processes are based on expensive excimer laser technology, and due to limitations in available wavelengths, not transferable to AlGaN LLO with higher band gaps. In this work, a femtosecond LLO technology is proposed and demonstrated to realize free-standing GaN LED chips. The used laser has a wavelength of 520 nm, a pulse length of 350 fs, and a repetition rate of 200 kHz. Even though the impinging photons have lower energy than the GaN bandgap (3.4 eV), the directed laser pulse is transmitted through the sapphire and reaches the interface to the n-GaN layer, where it is absorbed by non-linear two-photon excitation. Consequently, the GaN is decomposed resulting in lift-off from the sapphire. The LED selective-area transfer is performed using a two-step LLO process with different laser energies (Figure 1). From the experiments, InGaN/GaN LED chips with a total area of 1 × 1 mm² were successfully separated from the sapphire substrate (Figure 2), which exhibited an emission spectrum with peak wavelengths of ~465 nm in cathodoluminescence and electroluminescence measurements. Transmission electron microscopy was also used to verify the condition of InGaN/GaN multi-quantum wells (MQWs).

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.

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.

Chirped surface acoustic wave (SAW) resonators based on aluminum nitride (AlN) thin films have been designed and fabricated to comprehend the wave propagation characteristics induced by interdigitated transducers (IDTs) deposited on their surfaces. From the simulation results, design and geometry of the metal fingers including their width and pitch play critical roles on the wavelength of the acoustic wave and the mechanical displacement, which subsequently set the device resonant frequency. A single-step metal lift-off process involving photolithography and electron beam metal evaporation has been used to pattern and deposit Cr/Au IDT on AlN-on-Si wafers.