Silicon-tapered waveguide for mode conversion in metal-insulator-metal waveguide-based plasmonic sensor for refractive index sensing

In this study, we have undertaken a comprehensive numerical investigation of a refractive index sensor designed around a metal-insulator-metal (MIM) plasmonic waveguide. Our approach utilizes the finite element method to thoroughly analyze the sensor's performance. The sensor's configuration utilizes a ring resonator design, which has been slightly modified at the coupling segment. This modification enhances the efficiency of light coupling between a bus waveguide and the ring resonator, particularly at the resonance wavelength. This strategic adjustment significantly improves the device's extinction ratio, a critical factor in its functionality. Remarkably, the sensitivity of this sensor is determined to be approximately 1155.71 nm/RIU, while it possesses a figure of merit of 25.9. Furthermore, our study delves into the intricate mechanism governing the injection of light into the nanoscale MIM waveguide. We achieve this through the incorporation of silicon-tapered waveguides, which play a pivotal role in facilitating the transformation of a dielectric mode into a plasmonic mode, and vice versa. Ultimately, the findings of this research hold significant promise for advancing the field of plasmonic sensing systems based on MIM waveguide technology. The insights gained here pave the way for the practical realization and optimization of highly efficient and precise plasmonic sensors.

Numerical scrutiny of a silica-titania-based reverse rib waveguide with vertical and rounded sidewalls

In this work, a modal analysis of reverse rib waveguide (RRW) structures based on a silica-titania platform is carried out. The silica-titania waveguide films can be deposited via the sol-gel method and dip-coating technique. To combine this low-cost deposition technique with the economical fabrication method, we propose to structure the samples via wet-chemical etching. Due to the isotropic nature of wet etching, the waveguide architecture with rounded sidewalls is considered to model the RRW. Additionally, the modal conditions and bending loss are compared with the RRW with vertical sidewalls. It is assumed that this study will be beneficial for comprehending the modal conditions of waveguide structures with perfectly vertical and rounded sidewalls.

Development of a low-cost silica-titania optical platform for integrated photonics applications

This paper investigates a highly attractive platform for an optical waveguide system based on silica-titania material. The paper is organized into two parts. In the first part, an experimental study on the development of an optical waveguide system is conducted via the sol-gel dip-coating method, and the optical characterization of the waveguide system is performed at a visible wavelength. This system is capable of operating from visible to near-IR wavelength ranges. The experimental results prove the dominance of this waveguide platform due to its low-cost, low loss, and easy to develop integrated optics systems. The numerical analysis of a one-dimensional Photonic crystal waveguide optical filter based on the silica-titania platform is considered in the second part of the paper by utilizing the 2D-finite element method (2D-FEM). A Fabry-Perot structure is also analyzed for refractive index sensing applications. We believe that the results presented in this work will be valuable in the realization of low-cost photonic integrated circuits based on the silica-titania platform.

Plasmonic sensor based on metal-insulator-metal waveguide square ring cavity filled with functional material for the detection of CO2 gas

In this work, a straightforward and highly sensitive design of a CO₂ gas sensor is numerically investigated using the finite element method. The sensor is based on a plasmonic metal-insulator-metal (MIM) waveguide side coupled to a square ring cavity filled with polyhexamethylene biguanide (PHMB) functional material. The refractive index of the functional material changes when exposed to the CO₂ and that change is linearly proportional to the concentration of the gas. The sensors based on surface plasmon polariton (SPP) waves are highly sensitive due to the strong interaction of the electromagnetic wave with the matter. By utilizing PHMB polymer in the MIM waveguide plasmonic sensor provides a platform that offers the highest sensitivity of 135.95 pm/ppm which cannot be obtained via optical sensors based on silicon photonics. The sensitivity reported in this work is ∼7 times higher than reported in the previous works. Therefore, we believe that the results presented in this paper are exceedingly beneficial for the realization of the sensors for the detection of toxic gases by employing different functional materials.

327 Rare Synchronous Volvulus of Sigmoid Colon and Caecum, Management of Two Cases

Colonic volvulus accounts for approximately 5% of cases of large bowel obstruction. Sigmoid volvulus is commonest (75%), followed caecal volvulus (15%). Synchronous volvulus of the caecum and sigmoid is rare, with five reported cases in the literature. We report two cases in a London teaching hospital managed within 6 months. Both male patients (aged 72 and 79 years) had presented to the emergency department on multiple occasions (2-5 times in the preceding 1-8 months), with obstructive symptoms including tender abdominal distension and constipation. On all occasions, sigmoid volvulus was diagnosed based on plain abdominal films and flatus tubes were inserted, with initial clinical resolution. On their final presentation, both patients were admitted for definitive surgery. CT scans of the abdomen and pelvis were consistently reported as showing only sigmoid volvulus. Only intra-operatively was the diagnosis of synchronous caecal and sigmoid volvulus appreciated. Complete symptom resolution was achieved with subtotal colectomy and ileostomy formation. The key learning points from these cases are: 1) synchronous large bowel volvulus is a rare and easily missed diagnosis, 2) conservative management is unlikely to be successful, 3) radiological appearances may only suggest one type of large bowel volvulus and 4) definitive diagnosis is made intra-operatively.

Ultrashort inverted tapered silicon ridge-to-slot waveguide coupler at 1.55 µm and 3.392 µm wavelength

Herein, a compact and efficient inverted tapered ridge-to-slot waveguide coupler design based on the silicon-on-insulator platform is presented. The proposed device consists of three segments such as ridge waveguide, inverted taper segment, and slot waveguide. The coupling segment resembles a V shape, which provides good mode-matching between the ridge and slot waveguide. Two significant aspects of the proposed coupler design are discussed. In the first part of the paper, the coupler design optimized at 1.55 µm is suggested for optical interconnect. The propagation loss and coupling efficiency of 1.69 dB/µm and 91% are obtained for the 100 nm long tapered segment introduced between the ridge waveguide and slot waveguide, respectively. This propagation loss of the device includes the loss suffered by the ridge waveguide, tapered segment, and slot waveguide. Our proposed device design can be used in integrated optical platforms, where the efficient coupling of light to slot waveguides is required. Whereas, in the second part, the coupler design is optimized at the mid-infrared of 3.392 µm for an evanescent field absorption methane gas sensor. Slot waveguide offers excessive light-matter interaction due to its strong mode confinement in the low index material. The evanescent field ratio of ∼0.73 is obtained for the optimized waveguide geometry. As a result, 3 dB decay in the transmitted power can be obtained at 60% of gas concentration present in the ambient medium.

Long-term outcomes of the randomized controlled trial comparing 5-aminolaevulinic acid and Photofrin photodynamic therapy for Barrett's oesophagus related neoplasia

OBJECTIVE

Photodynamic therapy (PDT) was used as therapy for early neoplasia associated with Barrett's oesophagus (BE). This is 5-year follow-up of patients enrolled into randomised controlled trial of 5-aminolaevulinic acid (ALA) vs. Photofrin PDT.

METHODS

Biopsies were taken from original Barrett's segment during endoscopic follow up using Seattle protocol. Endoscopic mucosal resection (EMR) ± radiofrequency ablation (RFA) was preferred therapy in patients who failed PDT and/or had recurrent neoplasia.

RESULTS

Fifty eight of 64 patients enrolled in the original trial were followed up including 31 patients treated with ALA PDT (17 patients with ≤6 cm, 14 patients with >6 cm segment of BE) and 27 treated with Photofrin PDT (14 patients with ≤6 cm, 13 patients with >6 cm BE). Initial success was achieved in 65% (20/31) ALA and 48% (13/27) Photofrin patients (p = .289). Thirty five percent patients (7/20) relapsed in ALA group and 54% (7/13) relapsed in Photofrin group (p = .472). At a median follow-up of 67 months, no significant difference was found in long-term complete reversal of intestinal metaplasia (CR-IM) and complete reversal of dysplasia (CR-D) between ALA and Photofrin groups (78% vs. 63%; p = .18; 90% vs. 76%; p = .26). Original length of BE did not alter long-term outcome. Four patients from each group progressed to invasive oesophageal adenocarcinoma. Initial success of ALA PDT was associated with significantly better likelihood of long-term remission (p = .03).

CONCLUSIONS

Initial response to PDT plays key role in long term outcome. RFA ± EMR have, however, become preferred minimally invasive ablative therapy for BE-related neoplasia due to poor efficacy of PDT.

Using antibody directed phototherapy to target oesophageal adenocarcinoma with heterogeneous HER2 expression

Early oesophageal adenocarcinoma (OA) and pre-neoplastic dysplasia may be treated with endoscopic resection and ablative techniques such as photodynamic therapy (PDT). Though effective, discrete areas of disease may be missed leading to recurrence. PDT further suffers from the side effects of off-target photosensitivity. A tumour specific and light targeted therapeutic agent with optimised pharmacokinetics could be used to destroy residual cancerous cells left behind after resection. A small molecule antibody-photosensitizer conjugate was developed targeting human epidermal growth factor receptor 2 (HER2). This was tested in an in vivo mouse model of human OA using a xenograft flank model with clinically relevant low level HER2 expression and heterogeneity. In vitro we demonstrate selective binding of the conjugate to tumour versus normal tissue. Light dependent cytotoxicity of the phototherapy agent in vitro was observed. In an in vivo OA mouse xenograft model the phototherapy agent had desirable pharmacokinetic properties for tumour uptake and blood clearance time. PDT treatment caused tumour growth arrest in all the tumours despite the tumours having a clinically defined low/negative HER2 expression level. This new phototherapy agent shows therapeutic potential for treatment of both HER2 positive and borderline/negative OA.

Upregulation of mucin glycoprotein MUC1 in the progression to esophageal adenocarcinoma and therapeutic potential with a targeted photoactive antibody-drug conjugate

BACKGROUND

Mucin glycoprotein 1 (MUC1) is a glycosylated transmembrane protein on epithelial cells. We investigate MUC1 as a therapeutic target in Barrett's epithelium (BE) and esophageal adenocarcinoma (EA) and provide proof of concept for a light based therapy targeting MUC1.

RESULTS

MUC1 was present in 21% and 30% of significantly enriched pathways comparing BE and EA to squamous epithelium respectively. MUC1 gene expression was x2.3 and x2.2 higher in BE (p=<0.001) and EA (p=0.03). MUC1 immunohistochemical expression increased during progression to EA and followed tumor invasion. HuHMFG1 based photosensitive antibody drug conjugates (ADC) showed cell internalization, MUC1 selective and light-dependent cytotoxicity (p=0.0006) and superior toxicity over photosensitizer alone (p=0.0022).

METHODS

Gene set enrichment analysis (GSEA) evaluated pathways during BE and EA development and quantified MUC1 gene expression. Immunohistochemistry and flow cytometry evaluated the anti-MUC1 antibody HuHMFG1 in esophageal cells of varying pathological grade. Confocal microscopy examined HuHMFG1 internalization and HuHMFG1 ADCs were created to deliver a MUC1 targeted phototoxic payload.

CONCLUSIONS

MUC1 is a promising target in EA. Molecular and light based targeting of MUC1 with a photosensitive ADC is effective in vitro and after development may enable treatment of locoregional tumors endoscopically.

A HER2 selective theranostic agent for surgical resection guidance and photodynamic therapy

In many cancers early intervention involves surgical resection of small localised tumour masses. Inadequate resection leads to recurrence whereas overzealous treatment can lead to organ damage. This work describes production of a HER2 targeting antibody Fab fragment dual conjugated to achieve both real time near-infrared fluorescent imaging and photodynamic therapy. The use of fluorescence emission from a NIR-dye could be used to guide resection of tumour bulk, for example during endoscopic diagnosis for oesophago-gastric adenocarcinoma, this would then be followed by activation of the photodynamic therapeutic agent to destroy untreated localised areas of cancer infiltration and tumour infiltrated lymph nodes. This theranostic agent was prepared from the Fab fragment of trastuzumab initially by functional disulfide re-bridging and site-specific click reaction of a NIR-dye. This was followed by further reaction with a novel pre-activated form of the photosensitiser chlorin e6 with the exposed fragments' lysine residues. Specific binding of the theranostic agent was observed in vitro with a HER2 positive cell line and cellular near-infrared fluorescence was observed with flow cytometry. Specific photo-activity of the conjugates when exposed to laser light was observed with HER2 positive but not HER2 negative cell lines in vitro, this selectivity was not seen with the unconjugated drug. This theranostic agent demonstrates that two different photo-active functions can be coupled to the same antibody fragment with little interference to their independent activities.

Esophageal neoplasia arising from subsquamous buried glands after an apparently successful photodynamic therapy or radiofrequency ablation for Barrett's associated neoplasia

OBJECTIVE

Photodynamic therapy (PDT) and radiofrequency ablation (RFA) are effective non-surgical options for the treatment of Barrett's esophagus (BE) associated neoplasia. Development of subsquamous intestinal metaplasia after successful PDT and/or RFA is a recognized phenomenon; however, the occurrence of neoplasia arising from buried glands is a rare complication.

METHODS

This is a prospective case series of patients treated with PDT and/or RFA from 1999 to 2014 at University College London Hospital for neoplasia associated with BE, whose outcomes were analyzed retrospectively. Prior to any ablative therapy any visible nodularity was removed with endoscopic mucosal resection (EMR). After successful PDT and/or HALO RFA treatment, defined as a complete reversal of dysplasia and metaplasia, patients underwent endoscopic follow up using the Seattle protocol.

RESULTS

A total of 288 patients were treated, 91 with PDT between 1999 and 2010, 173 with RFA between 2007 and 2014, and 24 with both PDT and RFA for neoplasia associated with BE. Subsquamous neoplasia occurred in seven patients (7/288, 2%). The first patient developed subsquamous invasive adenocarcinoma and underwent curative surgery. Another five patients with subsquamous neoplasia (either high-grade dysplasia or intramucosal cancer) were treated successfully with EMR. The final patient developed subsquamous invasive esophagogastric junctional adenocarcinoma with liver metastases.

CONCLUSION

Development of subsquamous neoplasia after an apparently successful PDT and/or RFA is a rare but recognized complication. Clinicians should be aware of this phenomenon and have a low threshold for performing an EMR. Thorough surveillance following successful PDT and/or RFA ensuring high-quality endoscopy is required.

Improvement over time in outcomes for patients undergoing endoscopic therapy for Barrett's oesophagus-related neoplasia: 6-year experience from the first 500 patients treated in the UK patient registry

BACKGROUND

Barrett's oesophagus (BE) is a pre-malignant condition leading to oesophageal adenocarcinoma (OAC). Treatment of neoplasia at an early stage is desirable. Combined endoscopic mucosal resection (EMR) followed by radiofrequency ablation (RFA) is an alternative to surgery for patients with BE-related neoplasia.

METHODS

We examined prospective data from the UK registry of patients undergoing RFA/EMR for BE-related neoplasia from 2008 to 2013. Before RFA, visible lesions were removed by EMR. Thereafter, patients had RFA 3-monthly until all BE was ablated or cancer developed (endpoints). End of treatment biopsies were recommended at around 12 months from first RFA treatment or when endpoints were reached. Outcomes for clearance of dysplasia (CR-D) and BE (CR-IM) at end of treatment were assessed over two time periods (2008-2010 and 2011-2013). Durability of successful treatment and progression to OAC were also evaluated.

RESULTS

508 patients have completed treatment. CR-D and CR-IM improved significantly between the former and later time periods, from 77% and 56% to 92% and 83%, respectively (p<0.0001). EMR for visible lesions prior to RFA increased from 48% to 60% (p=0.013). Rescue EMR after RFA decreased from 13% to 2% (p<0.0001). Progression to OAC at 12 months is not significantly different (3.6% vs 2.1%, p=0.51).

CONCLUSIONS

Clinical outcomes for BE neoplasia have improved significantly over the past 6 years with improved lesion recognition and aggressive resection of visible lesions before RFA. Despite advances in technique, the rate of cancer progression remains 2-4% at 1 year in these high-risk patients.

TRIAL REGISTRATION NUMBER

ISRCTN93069556.