Challenges and Recent Analytical Advances in Micro/Nanoplastic Detection.

Despite growing ecological concerns, studies on microplastics and nanoplastics are still in their initial stages owing to technical hurdles in analytical techniques, especially for nanoplastics. We provide an overview of the general attributes of micro/nanoplastics in natural environments and analytical techniques commonly used for their analysis. After demonstrating the analytical challenges associated with the identification of nanoplastics due to their distinctive characteristics, we discuss recent technological advancements for detecting nanoplastics.

Exercise before pregnancy exerts protective effect on prenatal stress-induced impairment of memory, neurogenesis, and mitochondrial function in offspring.

Stress during pregnancy has a negative effect on the fetus. However, maternal exercise has a positive effect on the cognitive function of the fetus and alleviates the negative effects of stress. This study aimed to demonstrate whether exercise before pregnancy has a protective effect on prenatal stress-induced impairment of memory, neurogenesis and mitochondrial function in mice offspring. In this experiment, immunohistochemistry, Western blot, measurement of mitochondria oxygen respiration, and behavior tests were performed. Spatial memory and short-term memory of the offspring from the prenatal stress with exercise were increased compared to the offspring from the prenatal stress. The numbers of doublecortin-positive and 5-bromo-2'-deoxyuridine-positive cells in the hippocampal dentate gyrus of the offspring from the prenatal stress with exercise were higher compared to the offspring from the prenatal stress. The expressions of brain-derived neurotrophic factor, postsynaptic density 95 kDa, and synaptophysin in the hippocampus of the offspring from the prenatal stress with exercise were enhanced compared to the offspring from the prenatal stress. Oxygen consumption of the offspring from the prenatal stress with exercise were higher compared to the offspring from the prenatal stress. Exercise before pregnancy alleviated prenatal stress-induced impairment of memory, neurogenesis, and mitochondrial function. Therefore, exercise before pregnancy may have a protective effect against prenatal stress of the offspring.

Ultrahigh Nonlinear Responses from MXene Plasmons in the Short-Wave Infrared Range.

Surface plasmons in 2D materials such as graphene exhibit exceptional field confinement. However, the low electron density of majority of 2D materials, which are semiconductors or semimetals, has limited their plasmons to mid-wave or long-wave infrared regime. This study demonstrates that a 2D Ti3C2Tx MXene with high electron density can not only support strong plasmon confinement with an acoustic plasmon mode in the short-wave infrared region, but also provide ultrahigh nonlinear responses. The acoustic MXene plasmons (AMPs) in the MXene (Ti3C2Tx)-insulator (SiO2)-metal (Au) nanostructure generate in the 1.5-6.0 µm wavelength range, exhibiting a two orders of magnitude reduction in wavelength compared to wavelength in free space. Furthermore, AMP resonators with patterned Au rods exhibit a record-high nonlinear absorption coefficient of 1.37 × 10-2 m W-1 at wavelength of 1.56 µm, ≈3 orders of magnitude greater than the highest value recorded for other 2D materials. These results indicate that MXenes can overcome fundamental plasmon wavelength limitations of previously studied 2D materials, providing groundbreaking opportunities in nonlinear optical applications, including all-optical processing and ultrafast optical switching.

Enhancing Post-Surgical Rehabilitation Outcomes in Patients with Chronic Ankle Instability: Impact of Subtalar Joint Axis Balance Exercises Following Arthroscopic Modified Broström Operation.

Background and Objectives: This study aimed to evaluate the effects of subtalar joint axis-based balance exercises on the anterior talofibular ligament (ATFL) thickness, ankle strength, and ankle stability after an arthroscopic modified Broström operation (AMBO) for chronic ankle instability (CAI). Materials and Methods: The study included 47 patients diagnosed with CAI who underwent AMBO and were randomly divided into three groups: control (n = 11), general balance exercise (n = 17), and subtalar joint axis balance exercise (n = 19), regardless of the affected area. Participants in the exercise rehabilitation group performed exercises for 60 min twice a week for six weeks, starting six weeks after AMBO. ATFL thickness, ankle strength, and ankle dynamic stability were measured using musculoskeletal ultrasonography, Biodex, and Y-balance test, respectively, before and after treatment. Results: Compared with the remaining groups, the subtalar joint axis balance exercise group had reduced ATFL thickness (p = 0.000), improved ankle strength for eversion (p = 0.000) and inversion (p = 0.000), and enhanced ankle stability (p = 0.000). Conclusions: The study results suggest that subtalar joint axis-based balance exercises may contribute to the early recovery of the ankle joint after AMBO.

The Role of Reactive Oxygen Species, Inflammation, and Endoplasmic Reticulum Stress Response in the Finasteride Protective Effect against Benign Prostate Hyperplasia.

PURPOSE: Benign prostate hyperplasia (BPH) is a common age-related chronic condition. Its pathogenesis involves androgen imbalance, inflammation, oxidative stress, and endoplasmic reticulum (ER) stress. This study aims to assess the protective effect of finasteride, a 5α-reductase inhibitor, against testosterone propionate (TP)-induced BPH in rats and explore its potential mechanism of action. MATERIALS AND METHODS: TP-induced BPH rats received either saline or finasteride (1 mg/kg) orally once a day for 7 weeks. Prior to sacrificing the animals, blood samples were collected. After sacrifice, prostate and tissue around the prostate were dissected from seminal vesical for further analysis. Body weight, prostate weight, dihydrotestosterone (DHT), 5α-reductase type 2 (5-AR2), and prostate-specific antigen (PSA) levels were measured. In addition, HIF-1α, VEGF, MMP-2 expressions in prostate, oxidative stress, inflammation, and ER stress responses were analyzed to understand the mechanism of action of finasteride. RESULTS: Finasteride administration inhibited prostate enlargement, DHT, 5-AR2, and PSA levels in BPH rats. Additionally, finasteride inhibited angiogenesis markers such as HIF-1α, VEGF, and MMP-2. Moreover, components of oxidative stress, inflammation, and ER stress responses were significantly regulated by finasteride treatment. CONCLUSIONS: This study suggests that finasteride prevents BPH-associated symptoms by regulating angiogenesis, reactive oxygen species, ER stress responses, and inflammation, another mechanism to explain the effect of the 5α-reductase against BPH.

Effect of progressive resistance exercise using Thera-band on edema volume, upper limb function, and quality of life in patients with breast cancer-related lymphedema.

This study aimed to determine the effects of progressive resistive exercise (PRE), including complex decongestive physical therapy (CDPT), on edema volume, handgrip strength, upper extremity function, and quality of life (QoL) in patients with breast cancer-related lymphedema (BCRL). Twenty patients were randomized between the progressive resistance exercise group (PREG) and the self-home resistance exercise group (SREG). Two patients in each group dropped out of the study, leaving 16 patients: n=8 in the exercise group and n=8 in the SREG. First, the PREG and the SREG received CDPT. Subsequently, the patients in the PREG performed PRE, whereas the patients in the SREG performed self-home resistance exercises. Interventions were performed for 50 min, 3 times a week, for 6 weeks. The results showed that, for the edema volume, a significant intergroup variation was absent, whereas the intragroup variation was significant. The inter- and intragroup variations were significant for both handgrip strength and upper extremity function. Regarding QoL, a significant difference was observed in global health status/QoL and role function between the groups. Furthermore, significant differences were observed within the PREG in global health status/QoL; physical, role, and cognitive function; and dyspnea. No significant differences were observed within the SREG. The results collectively suggest that the exercise program was an intervention with a greater potential contribution to reducing edema and enhancing physical function in patients with BCRL.

Robotic-assisted simple prostatectomy after prostatic arterial embolization for large benign prostate hyperplasia: Initial experience.

Background and objective: We aimed to evaluate the safety and efficacy of robot-assisted simple prostatectomy (RASP) after prostatic arterial embolization (PAE) in large benign prostatic hyperplasia (BPH). Material and methods: This retrospective study included 11 cases of PAE and subsequent RASP, performed on 11 patients with BPH from March 2018 to September 2020. Clinical information on the patients was collected before surgery and 3 months after surgery. For the quantification of lower urinary tract symptoms (LUTS), International Prostate Symptom Scores (IPSSs), prostate-specific antigen (PSA) levels, urinary peak flow rate (Qmax), voided volume (Vvol), and postvoid residual volume (PVR) were measured. Results: PAE and the subsequent RASP were successfully performed in all 11 patients. The mean total prostate volume was 129.7 ± 65.1 mL, and the transitional zone volume was 71.7 ± 5.9 mL. The mean resected prostate volume was 60.8 ± 26.1 mL. The mean hemoglobin level of the patients prior to PAE was 14.2 ± 2.3 g/dL, and one day after RASP, the hemoglobin level was 12.4 ± 1.9 g/dL. The outcome indicated that there was a considerable decline in IPSS and PVR after RASP was performed compared to before PAE (21.6 ± 9.4 vs. 10.6 ± 8.0 and 159.4 ± 145.8 mL vs. 43.9 ± 45.9 mL). Qmax and Vvol significantly improved after RASP was performed (7.6 ± 5.2 mL/s vs. 26.1 ± 12.6 mL/s; 114.2 ± 92.5 mL vs. 192.4 ± 91.8 mL, respectively). Conclusion: This research demonstrated that RASP could be performed safely and effectively after PAE in patients with large BPH.

The Prevalence of Lower Urinary Tract Symptoms and Overactive Bladder in South Korea: A Cross-Sectional, Population-Based Study.

PURPOSE: Lower urinary tract symptoms (LUTS) affect over half of the adults' population worldwide, with an increasing prevalence among the older age groups. Therefore, with the increasing elderly population, LUTS is an important disease, highlighting the need for accurate data on its prevalence. This present study aimed to investigate the prevalence of LUTS in South Korea. METHODS: The study targeted individuals aged at least 19 years nationwide. We conducted computer-assisted telephone interviews, 80% mobile random digital dialing (RDD) sampling frame, and 20% landline RDD sampling frame between April and May 2020. Questionnaires included The International Prostate Symptom Score (IPSS), the overactive bladder symptom score (OABSS), and the characteristics of respondents. Current International Continence Society definitions were used for individual LUTS and OAB. RESULTS: There were 2,000 respondents, 1,009 (50.4%) were women and 546 (27.3%) were aged ≥60 years. Based on our IPSS questionnaire survey results, 77.9% of the respondents had LUTS; 63.7% had mild symptoms (1-7), 11.7% had moderate symptoms (8-19), and 2.4% had severe symptoms (20-35). The prevalence and severity of LUTS increased with age with 22.1% of respondents aged 60 years and above complaining of moderate or severe LUTS. According to the survey through OABSS, the prevalence of OAB was 9.6%, males were 10.3% and females were 9.0%. CONCLUSION: Based on our survey results, 77.9% of the Korean adult population (over the age of 19) experienced at least one LUTS, and the severity increased with age. The prevalence and severity of OAB increased with age, especially after 40 years; the prevalence of OAB was 9.6%, and 13.4% of them were over 60 years old.

Combined effects of aerobic exercise and 40-Hz light flicker exposure on early cognitive impairments in Alzheimer's disease of 3×Tg mice.

Alzheimer's disease (AD) is a progressive degenerative brain disease and the primary cause of dementia. At an early stage, AD is generally characterized by short-term memory impairment, owing to dysfunctions of the cortex and hippocampus. We previously reported that a combination of exercise and 40-Hz light flickering can protect against AD-related neuroinflammation, gamma oscillations, reduction in Aß, and cognitive decline. Therefore, we sought to extend our previous findings to the 5-mo-old 3×Tg-AD mouse model to examine whether the same favorable effects occur in earlier stages of cognitive dysfunction. We investigated the effects of 12 wk of exercise combined with 40-Hz light flickering on cognitive function by analyzing neuroinflammation, mitochondrial function, and neuroplasticity in the hippocampus in a 3×Tg-AD mouse model. Five-month-old 3×Tg-AD mice performed 12 wk of exercise with 40-Hz light flickering administered independently and in combination. Spatial learning and memory, long-term memory, hippocampal Aß, tau, neuroinflammation, proinflammatory cytokine expression, mitochondrial function, and neuroplasticity were analyzed. Aß and tau proteins levels were significantly reduced in the early stage of AD, resulting in protection against cognitive decline by reducing neuroinflammation and proinflammatory cytokines. Furthermore, mitochondrial function improved, apoptosis was reduced, and synapse-related protein expression increased. Overall, exercise with 40-Hz light flickering was significantly more effective than exercise or 40-Hz light flickering alone, and the improvement was comparable to the levels in the nontransgenic aged-match control group. Our results indicate a synergistic effect of exercise and 40-Hz light flickering on pathological improvements in the hippocampus during early AD-associated cognitive impairment.NEW & NOTEWORTHY Exercising in a 40-Hz light flicker environment was more effective than exercise or 40-Hz light flicker alone. This synergistic effect may prevent cognitive dysfunction by inhibiting Aß, tau pathway, and neuroinflammation and enhancing neuroplasticity and mitochondrial functions in the hippocampus during early Alzheimer's disease.

A Multicenter, Open-Label, Observational Study Evaluating the Quality of Life After Using a Hydrophilic-Coated Catheter (SpeediCath) With Self-Intermittent Catheterization.

PURPOSE: We evaluated the change in patient quality of life after the use of a hydrophilic-coated catheter (SpeediCath) in adults requiring intermittent catheterization (IC). METHODS: This was a multicenter, open-label, observational study using the Patient Perception of Intermittent Catheterization (PPIC) questionnaire and the Intermittent Self-Catheterization questionnaire (ISC-Q) and safety at 12 and 24 weeks in adult patients who had already used other type of catheters prior to switching to SpeediCath or in patients undergoing self-IC for the first time for any reason. RESULTS: Among a total of 360 subjects, 215 (59.7%) were women, and the mean age was 62.0±13.2 years. At 24 weeks, the satisfaction rate after using SpeediCath was 84.1%, and 80% of patients responded that they could easily perform IC. In total, 81.6% of patients were willing to continue using SpeediCath. The mean ISC-Q score was 54.90±18.65 at 24 weeks. Men found less interference in their daily life by performing IC than women and found it easier to handle the catheter before it was inserted into the urethra. At week 12, the mean change in ISC-Q was significantly greater in patients <65 years (20.24±23.55) than in those ≥65 years (7.57±27.70, P=0.049), but there was no difference at 24 weeks. The most common adverse events were urinary tract infection in 9.72%, gross hematuria in 2.78%, and urethral pain in 1.39%. CONCLUSION: The use of a SpeediCath provided good quality of life for patients who needed self-IC regardless of age or sex.

Can exercise-based cardiac rehabilitation increase physical activity in patients who have undergone total thoracoscopic ablation?

Evidence of the effect of exercise therapy in patients who have undergone total thoracoscopic ablation is lacking. This study aimed to evaluate the effects of eight weeks exercise-based cardiac rehabilitation on cardiopulmonary fitness and adherence to exercise in patients who underwent total thoracoscopic ablation and followed a regimen of exercise therapy. Twenty-four patients were involved in the study and were divided into two groups. The exercise group underwent exercise therapy, which included aerobic and resistance exercises, twice a week as part of an eight weeks hospital-based outpatient cardiac rehabilitation program. Cardiopulmonary exercise test was used to evaluate exercise capacity and the International Physical Activity Questionnaire was utilized to identify the amount of physical activity and confirm adherence to exercise at six months postoperatively. There were significant differences between the groups in moderate activity level (p = 0.004) and extent of total physical activity (p = 0.0001). Complications such as recurrent atrial fibrillation did not occur during the exercise training. Exercise-based cardiac rehabilitation was beneficial in maintaining the activity level at six months postoperatively. Early exercise intervention at four weeks post-surgical ablation is a safe and effective therapy that can increase physical activity. Further studies are needed to verify the effect of exercise intervention in a larger sample size of patients who have undergone total thoracoscopic ablation.

Treadmill Exercise Ameliorates Short-term Memory Impairment by Suppressing Hippocampal Neuroinflammation in Poloxamer-407-Induced Hyperlipidemia Rats.

PURPOSE: Poloxamer-407 (P-407) is used to induce hyperlipidemia. Exercise is effective in improving arteriosclerosis and cognitive impairment. In this research, the effect of treadmill running on short-term memory in the P-407-treated hyperlipidemia rats was studied focusing on neuroinflammation. METHODS: Rats were classified in normal group, normal and treadmill exercise group, P-407-treated group, and P-407-treated and treadmill exercise group. Hyperlipidemia rats were made by single intraperitoneal injection with P-407 (500 mg/kg). Treadmill exercise was conducted for 30 minutes once a day, 5 days per week during 28 days. Step-down avoidance task was done to measure short-term memory. Glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1 were assessed by immunohistochemistry. Expression of adhesion molecules and proinflammatory cytokines was determined by western blot analysis. RESULTS: Treadmill exercise alleviated lipid profiles in the P-407-induced hyperlipidemia rats. Treadmill exercise improved short-term memory, inhibited reactive astrogliosis and microglia activation, and suppressed expression of adhesion molecules and proinflammatory cytokines in the hyperlipidemic rats. CONCLUSION: Treadmill exercise exerts alleviating effect on memory deficits by inhibiting hippocampal neuroinflammation in the hyperlipidemia. The current results suggest that treadmill running serves as the treatment strategy for the cognitive dysfunction caused by hyperlipidemia.

Interventional benefit of Pilates using Oov and mat on middle-aged women with lower urinary tract symptoms: emphasis on abdominal muscle thickness and muscular function.

Lower urinary tract symptoms (LUTS) have been considered as clinically prevalent symptom in women, and can be ameliorated by the change of abdominal muscles and pelvic floor muscle (PFM). This study investigated the efficacy of Pilates program using Oov and mat on the change of abdominal muscle thickness, PFM function, and LUTS clinical score. 53 women experiencing LUTS were randomly assigned to Oov Pilates exercise group (OPEG) (n=20), mat Pilates exercise group (MPEG) (n= 16), and symptomatic control group (SCG) (n=17), respectively, and two groups using Oov and mat participated in 8-week Pilates program. Thickness of abdominal muscle, functional movement of PFM, and LUTS clinical score were measured from all groups. Thickness of rectus abdominis, internal oblique abdominis, transversus abdominis was significantly improved in OPEG (P<0.05), however, MPEG showed a significant change only in transversus abdominis (P<0.05). In all abdominal muscles, OPEG had a significantly improved abdominal muscle thickness compared to SCG (P<0.05). Functional movement of PFM in OPEG was significantly decreased (P<0.005), but not in MPEG and SCG. In LUTS clinical score, OPEG and MPEG showed a significantly abated symptoms in degree of voiding-related symptoms and discomfort (P<0.005), but not in SCG. Our study highlighted that Pilates using Oov can be an effective intervention to ameliorate the quantitative quality of abdominal muscle thickness and PFM, which ultimately provides the satisfied self-clinical index in degree of voiding-related symptoms and discomfort.

Reduction of Electrochemically Exfoliated Graphene Films for High-Performance Electromagnetic Interference Shielding.

Two-dimensional graphene is of great interest for electromagnetic interference (EMI) shielding owing to its inherent electrical conductivity, lightweight, and excellent mechanical flexibility even at minor thicknesses. However, the complex synthesis and quality-control difficulties limit its application. In this study, we demonstrate that electrochemically exfoliated graphene (EEG) with post-reduction treatment is a promising candidate for lightweight EMI shielding materials. A facile electrochemical exfoliation approach produces a high-quality multilayer graphene with a high electrical conductivity of ∼600 S cm-1, owing to its low degree of oxidation. The reduction of EEG by three different methods, including chemical, thermal, and microwave treatments, causes the removal of surface functional groups as well as significant changes in the microstructure of the final films. The reduced graphene films by microwaves, which are driven by the improved electrical conductivity and large volume expansion, exhibit an EMI shielding effectiveness of 108 dB at a thickness of 125 µm, one of the largest EMI shielding values ever reported for graphene at comparable thicknesses.

Light Engineering in Nanometer Space.

Significant advances have been made in photonic integrated circuit technology, similar to the development of electronic integrated circuits. However, the miniaturization of cavity resonators, which are the essential components of photonic circuits, still requires considerable improvement. Over the past decades, various optical cavities have been utilized to implement next-generation light sources in photonic circuits with low energy, high data traffic, and integrable physical sizes. Nevertheless, it has been difficult to reduce the size of most commercialized cavities beyond the diffraction limit while maintaining high performance. Herein, recent advancements in subwavelength metallic cavities that can improve performance, even with the use of lossy plasmonic modes, are reviewed. The discussion is divided in three parts according to light engineering methods: subwavelength metal-clad cavities engineered using intermediate dielectric cladding; implementation of plasmonic cavities and waveguides using plasmonic crystals; and development of deep-subwavelength plasmonic waveguides and cavities using geometric engineering. A direction for further developments in photonic integrated circuit technology is also discussed, along with its practical application.

Extreme field confinement in zigzag plasmonic crystals.

We propose extreme field confinement in a zigzag plasmonic crystal that can produce a wide plasmonic bandgap near the visible frequency range. By applying a periodic zigzag structure to a metal-insulator-metal plasmonic waveguide, the lowest three plasmonic crystal bands are flattened, creating a high-quality broadband plasmonic mirror over a wavelength range of 526-909 nm. Utilizing zigzag plasmonic crystals in a three-dimensional tapered metal-insulator-metal plasmonic cavity, extreme field confinement with a modal volume of less than 0.00005 λ 3 can be achieved even at resonances over a wide frequency range. In addition, by selecting the number of zigzag periods in the plasmonic crystal, critical coupling between the cavity and the waveguide can be achieved, thereby maximizing the field intensity with an enhancement factor of 105 or more. We believe that zigzag plasmonic crystals will provide a powerful platform for implementing broadband on-chip plasmonic devices.

Anomalous absorption of electromagnetic waves by 2D transition metal carbonitride Ti3CNT x (MXene).

Lightweight, ultrathin, and flexible electromagnetic interference (EMI) shielding materials are needed to protect electronic circuits and portable telecommunication devices and to eliminate cross-talk between devices and device components. Here, we show that a two-dimensional (2D) transition metal carbonitride, Ti3CNT x MXene, with a moderate electrical conductivity, provides a higher shielding effectiveness compared with more conductive Ti3C2T x or metal foils of the same thickness. This exceptional shielding performance of Ti3CNT x was achieved by thermal annealing and is attributed to an anomalously high absorption of electromagnetic waves in its layered, metamaterial-like structure. These results provide guidance for designing advanced EMI shielding materials but also highlight the need for exploring fundamental mechanisms behind interaction of electromagnetic waves with 2D materials.

Treadmill Exercise Improves Motor Function and Short-term Memory by Enhancing Synaptic Plasticity and Neurogenesis in Photothrombotic Stroke Mice.

PURPOSE: Thrombotic stroke is a type of ischemic stroke characterized by motor dysfunction and memory impairments. In the present study, the effect of treadmill exercise on motor function and short-term memory was evaluated in relation with synaptic plasticity in the mice with photothrombotic stroke. METHODS: Photothrombotic stroke was induced by cortical photothrombotic vascular occlusion. The mice in the treadmill exercise groups performed running on a motorized treadmill for 28 days. Motor function was determined using rota-rod test and foot fault test. Step-through avoidance task was conducted to evaluate short-term memory. Immunohistochemistry for 5-bromo-2'-deoxyuridine and doublecortin was conducted to detect new cell generation. Postsynaptic density protein 95, synaptophysin, brain-derived neurotrophic factor (BDNF), and tyrosine kinase B receptor (TrkB) were determined using western blot. The number of dendritic spines was determined using Golgi stain. RESULTS: Treadmill exercise improved motor function and short-term memory in mice with the photothrombotic stroke. The infarct size was reduced and the number of dendritic spines and expression of postsynaptic density protein 95 and synaptophysin in the peri-infarct cortex and hippocampus were increased by treadmill exercise in photothrombotic stroke mice. Treadmill exercise enhanced neurogenesis through increasing the expression of the hippocampal BDNF and TrkB in photothrombotic stroke mice. CONCLUSION: Treadmill exercise improved motor function and short-term memory through increasing synaptic plasticity and neurogenesis in photothrombotic stroke mice. Treadmill exercise can be used as an effective treatment strategy to improve brain function related to stroke.

Beam steering of a single nanoantenna.

Nanoantennas play an important role as mediators to efficiently convert free-space light into localized optical energy and vice versa. However, effective control of the beam direction of a single nanoantenna remains a great challenge. In this paper, we propose an approach to steer the beam direction of a single nanoantenna by adjusting two antenna modes with opposite phase symmetry. Our theoretical study confirmed that the combination of even- and odd-symmetric modes with a phase difference of π/2 enables effective beam steering of a single nanoantenna whose steering angle is controlled by adjusting the amplitude ratio of the two antenna modes. To implement our theory in real devices, we introduced asymmetric trapezoidal nano-slot antennas with different side air-gaps of 10 and 50 nm. The trapezoidal nanoantennas can simultaneously excite the dipole and quadrupole modes in a single nanoantenna and enables effective beam steering with an angle of greater than 35° near the resonance of the quadrupole mode. In addition, the steering angle can also be controlled by adjusting the degree of asymmetry of the trapezoidal slot structure. We believe that our beam steering method for a single nanoantenna will find many potential applications in fields such as imaging, sensing, optical communication, and quantum optics.

Near-field transmission matrix microscopy for mapping high-order eigenmodes of subwavelength nanostructures.

As nanoscale photonic devices are densely integrated, multiple near-field optical eigenmodes take part in their functionalization. Inevitably, these eigenmodes are highly multiplexed in their spectra and superposed in their spatial distributions, making it extremely difficult for conventional near-field scanning optical microscopy (NSOM) to address individual eigenmodes. Here, we develop a near-field transmission matrix microscopy for mapping the high-order eigenmodes of nanostructures, which are invisible with conventional NSOM. At an excitation wavelength where multiple modes are superposed, we measure the near-field amplitude and phase maps for various far-field illumination angles, from which we construct a fully phase-referenced far- to near-field transmission matrix. By performing the singular value decomposition, we extract orthogonal near-field eigenmodes such as anti-symmetric mode and quadruple mode of multiple nano-slits whose gap size (50 nm) is smaller than the probe aperture (150 nm). Analytic model and numerical mode analysis validated the experimentally observed modes.