FedFwd: Federated Learning without Backpropagation

In federated learning (FL), clients with limited resources can disrupt the training efficiency. A potential solution to this problem is to leverage a new learning procedure that does not rely on backpropagation (BP). We present a novel approach to FL called FedFwd that employs a recent BP-free method by Hinton (2022), namely the Forward Forward algorithm, in the local training process. FedFwd can reduce a significant amount of computations for updating parameters by performing layer-wise local updates, and therefore, there is no need to store all intermediate activation values during training. We conduct various experiments to evaluate FedFwd on standard datasets including MNIST and CIFAR-10, and show that it works competitively to other BP-dependent FL methods.Comment: ICML 2023 Workshop (Federated Learning and Analytics in Practice: Algorithms, Systems, Applications, and Opportunities

Aptamer-functionalized Si-nanonet electrolyte-gate field-effect transistor (EGT) for detection of SARS-CoV-2 virus

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DC and AC Sensing Characteristics of a Si-nanowire BioFET for Urea Detection

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Hydrogel-coated nanonet-based field-effect transistors for SARS-CoV-2 spike protein detection in high ionic strength samples

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An Ultrasensitive Silicon-Based Electrolyte-Gated Transistor for the Detection of Peanut Allergens

The highly sensitive detection of peanut allergens (PAs) using silicon-based electrolyte-gated transistors (Si-EGTs) was demonstrated. The Si-EGT was made using a top-down technique. The fabricated Si-EGT showed excellent intrinsic electrical characteristics, including a low threshold voltage of 0.7 V, low subthreshold swing of <70 mV/dec, and low gate leakage of <10 pA. Surface functionalization and immobilization of antibodies were performed for the selective detection of PAs. The voltage-related sensitivity (SV) showed a constant behavior from the subthreshold regime to the linear regime. The current-related sensitivity (SI) was high in the subthreshold regime and then significantly decreased as the drain current increased. The limit of detection (LOD) was calculated to be as low as 25 pg/mL based on SI characteristics, which is the lowest value reported to date in the literature for various sensor methodologies. The Si-EGT showed selective detection of PA through a non-specific control test. These results confirm that Si-EGT is a high-sensitivity and low-power biosensor for PA detection

Improvement of Electrical Characteristics and Stability of Amorphous Indium Gallium Zinc Oxide Thin Film Transistors Using Nitrocellulose Passivation Layer

In this research, nitrocellulose is proposed as a new material for the passivation layers of amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs). The a-IGZO TFTs with nitrocellulose passivation layers (NC-PVLs) demonstrate improved electrical characteristics and stability. The a-IGZO TFTs with NC-PVLs exhibit improvements in field-effect mobility (μ_FE) from 11.72 ± 1.14 to 20.68 ± 1.94 cm²/(V s), threshold voltage (<i>V</i>_th) from 1.85 ± 1.19 to 0.56 ± 0.35 V, and on/off current ratio (<i>I</i>_on/off) from (5.31 ± 2.19) × 10⁷ to (4.79 ± 1.54) × 10⁸ compared to a-IGZO TFTs without PVLs, respectively. The <i>V</i>_th shifts of a-IGZO TFTs without PVLs, with poly­(methyl methacrylate) (PMMA) PVLs, and with NC-PVLs under positive bias stress (PBS) test for 10,000 s represented 5.08, 3.94, and 2.35 V, respectively. These improvements were induced by nitrogen diffusion from NC-PVLs to a-IGZO TFTs. The lone-pair electrons of diffused nitrogen attract weakly bonded oxygen serving as defect sites in a-IGZO TFTs. Consequently, the electrical characteristics are improved by an increase of carrier concentration in a-IGZO TFTs, and a decrease of defects in the back channel layer. Also, NC-PVLs have an excellent property as a barrier against ambient gases. Therefore, the NC-PVL is a promising passivation layer for next-generation display devices that simultaneously can improve electrical characteristics and stability against ambient gases

Hydrogel-gated silicon nanotransistors for SARS-CoV-2 antigen detection in physiological ionic strength

The recent COVID-19 outbreak has strongly pushed the field of biosensors, resulting in multiple new approaches for quantitative virus detection. Among them, those using nanostructured field-effect transistors (FETs) as transducers provide an ultrasensitive approach requiring simple setups for their miniaturization toward point-of-care diagnostics of the disease. However, this type of biosensors suffer from limited sensitivity when it comes to analyzing biofluids due to their shortened screening length in presence of complex liquids with high ionic strength. In this work we propose a solution to this problem, which consists on the surface modification of the FETs with a hydrogel based on star-shaped polyethylene glycol and loaded with specific antibodies against SARS-CoV-2 spike protein. The hydrogel increases the effective Debye length, allowing to preserve the sensitivity in high ionic strength solutions. We provide the demonstration employing silicon nanonet-based FETs for the detection of viral antigens in buffer and in saliva, as well as cultured viral particles. We finally discriminate positive and negative patient samples (nasopharyngeal swab), and propose the theoretical frame that discusses the mechanism of the sensitivity preservation based on the presence of the pegylated hydrogel

Sybodies as novel bioreceptors toward field-effect transistor-based detection of SARS-CoV-2 antigens

The SARS-CoV-2 pandemic has increased the demand for low-cost, portable and rapid biosensors, driving huge research efforts toward new nanomaterial-based approaches with high sensitivity. Many of them employ antibodies as bioreceptors, which have a costly development process requiring animal facilities. Recently, sybodies emerged as an alternative new class of synthetic binders/receptors with high antigen binding efficiency, improved chemical stability, and lower production costs via animal-free methods. Their smaller size is an important asset to consider in combination with ultrasensitive field-effect transistors (FETs) as transducers, which respond more intensely when the biorecognition occurs in close proximity to their surface. This work demonstrates the immobilization of sybodies against the spike protein of the virus on silicon surfaces, which are often the integral part of the semiconducting channel of FETs. Immobilized sybodies maintain the capability to capture antigens even at low concentrations in the femtomolar range, as observed by fluorescence microscopy. Finally, the first proof-of-concept of sybody-modified FET sensing is provided, using a nanoscopic silicon net as the sensitive area where the sybodies are immobilized. The future development of further sybodies against other biomarkers and their generalization in biosensors could be critical to decrease the cost of biodetection platforms in future pandemics

Creating Tunable Mesoporosity by Temperature???Driven Localized Crystallite Agglomeration

A new synthetic approach for tunable mesoporous metal???organic frameworks (MeMs) is developed. In this approach, mesopores are created in the process of heat conversion of highly mosaic metal???organic framework (MOF) crystals with non-interpenetrated low-density nanocrystallites into MOF crystals with two-fold interpenetrated high-density nanocrystallites. The two-fold interpenetration reduces the volume of the nanocrystallites in the mosaic crystal, and the accompanying localized agglomeration of the nanocrystallites results in the formation of mesopores among the localized crystallite agglomerates. The pore size can be easily modulated from 7 to 90 nm by controlling the heat treatment conditions, that is, the aging temperature and aging time. Various proteins can be encapsulated in the MeM, and immobilized enzymes show catalyst activity comparable to that of the free native enzymes. Immobilized ??-galactosidase is recyclable and the enzyme activity of the immobilized catalase is maintained after exposure to high temperatures and various organic solvents

Probing Conformational Change of Intrinsically Disordered α‑Synuclein to Helical Structures by Distinctive Regional Interactions with Lipid Membranes

α-Synuclein (α-Syn) is an intrinsically disordered protein, whose fibrillar aggregates are associated with the pathogenesis of Parkinson’s disease. α-Syn associates with lipid membranes and forms helical structures upon membrane binding. In this study, we explored the helix formation of α-Syn in solution containing trifluoroethanol using small-angle X-ray scattering and electrospray ionization ion mobility mass spectrometry. We then investigated the structural transitions of α-Syn to helical structures via association with large unilamellar vesicles as model lipid membrane systems. Hydrogen–deuterium exchange combined with electrospray ionization mass spectrometry was further utilized to understand the details of the regional interaction mechanisms of α-Syn with lipid vesicles based on the polarity of the lipid head groups. The characteristics of the helical structures were observed with α-Syn by adsorption onto the anionic phospholipid vesicles via electrostatic interactions between the N-terminal region of the protein and the anionic head groups of the lipids. α-Syn also associates with zwitterionic lipid vesicles and forms helical structures via hydrophobic interactions. These experimental observations provide an improved understanding of the distinct structural change mechanisms of α-Syn that originate from different regional interactions of the protein with lipid membranes and subsequently provide implications regarding diverse protein–membrane interactions related to their fibrillation kinetics