A high affinity and specificity anti-HER2 single-domain antibody (VHH) that targets trastuzumab's epitope with versatile biochemical, biological, and medical applications

In the past decade, various single-domain antibodies from llamas, also known as VHH or nanobody, have been discovered with applications in tumor imaging and cancer therapy. However, the potential application of anti-HER2 VHHs as a diagnostic tool suitable for ELISA, flow cytometry, cell imaging, bispecific antibody engineering, and immunohistochemistry has not been fully elucidated. To investigate this potential, HER2 antigen was expressed in HEK293 F cells, purified, and used to immunize llama. Using phage display, anti-HER2 VHHs with high affinity and specificity were isolated, sequenced, and constructed with a Histag and c-Myc tag. The constructed anti-HER2 VHHs were then expressed in E. coli, purified, and evaluated for their use in ELISA, flow cytometry, cell imaging, and immunohistochemistry. The affinities of the anti-HER2 VHHs toward the HER2 antigen were determined using biolayer interferometry. Furthermore, the binding sites of the anti-HER2 VHHs were evaluated by epitope mapping and in silico modeling and docking. Here, we report the sequence of an anti-HER2 VHH with high affinity (sub-nanomolar), specificity, and selectivity. This VHH binds to the same epitope as trastuzumab and can be utilized to generate bispecific antibodies or used as a diagnostic tool to differentiate HER2+ from HER2- antigens on plates, cells, and tissues. This discovery has broad applications in biochemical, biological, and medical sciences.

Deep phenotyping of the neuroimaging and skeletal features in KBG syndrome: a study of 53 patients and review of the literature

BACKGROUND

KBG syndrome is caused by haploinsufficiency of ANKRD11 and is characterised by macrodontia of upper central incisors, distinctive facial features, short stature, skeletal anomalies, developmental delay, brain malformations and seizures. The central nervous system (CNS) and skeletal features remain poorly defined.

METHODS

CNS and/or skeletal imaging were collected from molecularly confirmed individuals with KBG syndrome through an international network. We evaluated the original imaging and compared our results with data in the literature.

RESULTS

We identified 53 individuals, 44 with CNS and 40 with skeletal imaging. Common CNS findings included incomplete hippocampal inversion and posterior fossa malformations; these were significantly more common than previously reported (63.4% and 65.9% vs 1.1% and 24.7%, respectively). Additional features included patulous internal auditory canal, never described before in KBG syndrome, and the recurrence of ventriculomegaly, encephalic cysts, empty sella and low-lying conus medullaris. We found no correlation between these structural anomalies and epilepsy or intellectual disability. Prevalent skeletal findings comprised abnormalities of the spine including scoliosis, coccygeal anomalies and cervical ribs. Hand X-rays revealed frequent abnormalities of carpal bone morphology and maturation, including a greater delay in ossification compared with metacarpal/phalanx bones.

CONCLUSION

This cohort enabled us to describe the prevalence of very heterogeneous neuroradiological and skeletal anomalies in KBG syndrome. Knowledge of the spectrum of such anomalies will aid diagnostic accuracy, improve patient care and provide a reference for future research on the effects of ANKRD11 variants in skeletal and brain development.

ANKRD11 pathogenic variants and 16q24.3 microdeletions share an altered DNA methylation signature in patients with KBG syndrome

Pathogenic variants in ANKRD11 or microdeletions at 16q24.3 are the cause of KBG syndrome (KBGS), a neurodevelopmental syndrome characterized by intellectual disability, dental and skeletal anomalies, and characteristic facies. The ANKRD11 gene encodes the ankyrin repeat-containing protein 11A transcriptional regulator, expressed in the brain and implicated in neural development. Syndromic conditions caused by pathogenic variants in epigenetic regulatory genes show unique patterns of DNA methylation (DNAm) in peripheral blood termed DNAm signatures. Given ANKRD11’s role in chromatin modification, we tested whether pathogenic ANKRD11 variants underlying KBGS are associated with a DNAm signature. We profiled whole-blood DNAm in 21 individuals with ANKRD11 variants, 2 individuals with microdeletions at 16q24.3, and 28 typically developing individuals, using Illumina’s Infinium EPIC array. We identified 95 differentially methylated CpG sites that distinguished individuals with KBGS and pathogenic variants in ANKRD11 (n = 14) from typically developing controls (n = 28) and was also validated in seven additional individuals with pathogenic ANKRD11 variants. We generated a machine learning model from the KBGS DNAm signature and classified the DNAm profiles of 4 individuals with variants of uncertain significance (VUS) in ANKRD11. We identified an intermediate classification score for an inherited missense variant transmitted from a clinically unaffected mother to her affected child. In conclusion, we show the DNAm profile of two individuals with 16q24.3 microdeletions, was indistinguishable from the DNAm profile of individuals with pathogenic variants in ANKRD11 and we demonstrate the diagnostic utility of the new KBGS signature by classifying the DNAm profiles of individuals with VUS in ANKRD11.

A Collective Intelligence Platform to Support Older Cancer Survivors: Towards the Definition of LifeChamps System and Big Data Reference Architecture

Within the most recent years, most of the cancer patients are older age, which implies the necessity to a better understanding of aging and cancer connection. This work presents the LifeChamps solution built on top of cutting-edge Big Data architecture and HPC infrastructure concepts. An innovative architecture was envisioned supported by the Big Data Value Reference Model and answering the system requirements from high to low level and from logical to physical perspective, following the "4+1 architectural model".

Hi-C Identifies Complex Genomic Rearrangements and TAD-Shuffling in Developmental Diseases

Genome-wide analysis methods, such as array comparative genomic hybridization (CGH) and whole-genome sequencing (WGS), have greatly advanced the identification of structural variants (SVs) in the human genome. However, even with standard high-throughput sequencing techniques, complex rearrangements with multiple breakpoints are often difficult to resolve, and predicting their effects on gene expression and phenotype remains a challenge. Here, we address these problems by using high-throughput chromosome conformation capture (Hi-C) generated from cultured cells of nine individuals with developmental disorders (DDs). Three individuals had previously been identified as harboring duplications at the SOX9 locus and six had been identified with translocations. Hi-C resolved the positions of the duplications and was instructive in interpreting their distinct pathogenic effects, including the formation of new topologically associating domains (neo-TADs). Hi-C was very sensitive in detecting translocations, and it revealed previously unrecognized complex rearrangements at the breakpoints. In several cases, we observed the formation of fused-TADs promoting ectopic enhancer-promoter interactions that were likely to be involved in the disease pathology. In summary, we show that Hi-C is a sensible method for the detection of complex SVs in a clinical setting. The results help interpret the possible pathogenic effects of the SVs in individuals with DDs.

Access to breast/ovarian genetic testing: 20 years of a multidisciplinary program

e14015

Background: After institutional and ethical review, a multidisciplinary Breast/Ovarian Cancer Family Risk program started in January 2000. Core team included medical oncologists, molecular biologists, medical geneticists and specialized nurses. Besides access to genetic testing (GT), predictive risk analysis and tailored surveillance plans were provided for women without criteria for GT, and carriers of germline pathogenic/likely pathogenic variants (PV/LPV) were included in prospective follow up. Methods: Descriptive statistics concerning patients (pts), medical visits and genetic tests performed under the program from January 2000-December 2019. Results:A total of 28400 medical appointments (including multidisciplinary meetings with radiology, breast and plastic surgery and gynecology) were performed for 10100 pts: 9281 women (92%) and 819 men (8%), with an average of 46,0 years (45,6 and 51,1 respectively). Most pts were referred from our cancer center or were invited for cascade testing (8044, 79,6%), although we accepted referrals from external health services (2056 pts). GT: 5665 tests performed (4454 for index pts (IP) and 1211 for family relatives); 3170 (71%) IP consented only in BRCA1/2 and 1284 IP (29%) in sequential/panel testing. Detection rate for IP testing was 12,5% [440 BRCA1/2; 118 Other Hereditary Syndromes (OSH)]. OHS IP: CHEK2(32), ATM(14), TP53(11), MUTYH(12), PALB2(10), RAD51D(10), RAD51C(9), BLM(5), BRIP1(4), RAD50 (4), PTEN(2), MSH2(2), MLH1(1) FAM175A(1), BARD1(1). Six- hundred and twenty-six IP with previous inconclusive results consented on panel testing and 62(9,9%) were diagnosed with a non- BRCA1/2 PV/LPV. Until June 2019, 915 BRCA1/2 pts were included in a registry for prospective follow up. Conclusions: our program has allowed for access to Breast/Ovarian GT and risk management in the National Health Service, for the past 20 years. Twenty per cent of all pts are referrals from external health services. The ever increasing challenges to the resources of the program include: new indications for GT, the increase in priority pts for GT due to more therapy options, risk dynamics in previous registered families, evolving molecular methodologies and the management of families with complex genetic variants. The growing number of pts, including men, led to a recent change in the label of the program (Breast/Ovarian/Prostate Cancer Family Risk) and new approaches to promote access of specific populations to GT (like telegenetics) are being tested.

Abstract P6-08-17: When BRCA2-breast cancer is more prevalent than BRCA1-breast cancer: Prospective follow-up data from a multidisciplinary program

PURPOSERecent studies questioned the role of BRCA2 as a prognostic factor. Although differences between clinicopathological characteristics of BRCA1-breast cancer (BC) and BRCA2-BC have been described, long-term follow-up data related to prognosis and survival is lacking. We report the analysis of our cohort of BRCA1/2-BC patients (pts) included in our multidisciplinary program. This cohort includes BRCA2-BC c.156_157insAlu carriers, which was previously described as a Portuguese founder mutation.

PATIENTS AND METHODS

All pts underwent comprehensive BRCA1/2 testing. Data was obtained from all BRCA1/2 pts included in prospective follow up from January 2000 to June 2019, with BC as first cancer diagnosis. Follow-up started after genetic testing.

RESULTSFrom 5504 cases (4021 index, 1483 family relatives) that consented on BRCA1/2 testing, 613 BRCA1/2 were cancer pts, of which 478 (78%) had BC as their first cancer diagnosis. These were mostly BRCA2 (n=321, 67.2% vs BRCA1 n=156, 32.6%) females (95.2%), and 129 (40%) of all BRCA2 cases were 156_157insAlu. Three pts had double pathogenic mutations (BRCA1+CHEK2, BRCA2+CHEK2 and BRCA1+BRCA2). Median follow-up was 4.3 yrs (0-17.8).Median age at testing was 50.3 (21-84) yrs and median age at BC diagnosis was significantly higher for BRCA2-BC (45.9 (21-80) vs 42.7 yrs (28-65), p<0.02) than for BRCA1-BC. Compared to BRCA1 pts, BRCA2 pts had higher prevalence of tumors <1cm at diagnosis (10.6% vs 5.8%, p=0.057), hormone receptor positive status (60.4% vs 28.8%, p<0.0001), and lower prevalence of TN phenotype (9.3% vs 48.7%, p<0.0001). BRCA2-BC was associated with longer median time to relapse (TTR) (63.6m, 95% CI 43.1-84.2, vs 23.3m, 95% CI 18.6-28.5, p<0.05), even if relapse rates were similar (9.9% vs 9.6%) and, for a median follow up of 4.3 yrs, no statistically significant difference for survival was observed (7.2 yrs (95% CI 4.1-10.3) vs 5.9 yrs (95% CI 3.8-7.9) for BRCA2-BC and BRCA1-BC respectively).Uptake of preventive surgeries (bilateral or contralateral mastectomy*, adnexectomy, or both) was similar between both groups (BRCA2 17.8%, 27.1% and 11.5% vs BRCA1 18.6%, 26.9% and 10.9%, respectively). Subsequent cancers occurred in 169 pts (35.4%), and were mostly BC (BRCA2 69.1% vs BRCA1 58.7%). Having subsequent cancer was associated with BRCA2 status (72.8% vs 27.2%, p<0.04), not undergoing risk-reducting mastectomy (91.7% vs 8.3%, p<0.0001) and not undergoing risk-reducting mastectomy with bilateral anexectomy (95.3% vs 4.7%, p=0.001). Regarding subsequent cancers, 116 cases were detected during prospective follow-up, 89 in 66 BRCA2-BC and [CB1] 27 cancers in 27 BRCA1-BC.

CONCLUSIONIn our population, there is a higher prevalence of BRCA2-BC than BRCA1-BC, not completely explained by the founder effect of c.156_157insAlu. For the described follow up, TTR was longer for BRCA2-BC pts but survival was not different between the two groups, even though BRCA2 status was associated with more subsequent cancer diagnoses. As expected, preventive surgeries were inversely associated with second cancers. Data on prognosis and survival needs to be confirmed with longer follow up. *- includes pts previously treated with conservative surgery

Citation Format: Catarina Bexiga, Priscila Nejo, Inês Oliveira, Paula Rodrigues, Patrícia Pereira, Sofia Fragoso, Alexandra Mayer, Joana Parreira, Sidónia Santos, Pedro Louro, Ana Luís, Sandra Bento, Isália Miguel, Cecília Moura, Ana Clara, Fátima Vaz. When BRCA2-breast cancer is more prevalent than BRCA1-breast cancer: Prospective follow-up data from a multidisciplinary program [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-08-17.

Abstract P6-08-36: Uptake of preventive surgeries in a prospective cohort of BRCA1/2 healthy women

PURPOSE

Previous studies referred to uptake of preventive surgeries (PS) in BRCA1/2 healthy carriers in ages older than recommended (35yrs). Since our population has a higher prevalence of BRCA2 mutations (usually associated with an older age at Breast Cancer diagnosis) we proposed to study ages and type of preventive surgeries uptaken by BRCA1/2 women included in prospective follow up.

PATIENTS AND METHODS

Review of all healthy (without a previous cancer diagnosis) BRCA1/2 carriers included in our program from January 2000 to June 2019. Follow-up started after genetic testing. Men were excluded from this analysis.

RESULTS

A total of 5504 cases (4021 index, 1483 relatives) consented for BRCA1/2 testing. We identified 238 healthy BRCA1/2 carriers (BRCA2:158 (66.4%) vs BRCA1 80 (33.6%). Median age at genetic diagnosis was 38.9 yrs (16-78). With a median follow up of 4yrs, bilateral adnexectomy (BA) was the most frequent PS observed (45 BRCA2 and 28 BRCA1 cases) with 15/45 % and 6/28% undergoing BA and bilateral mastectomy (BM) simultaneously. Bilateral mastectomy was uptaken by 14% BRCA2 women and 10% BRCA1 women. Median ages for PS were: BRCA2-AB: 47,4 (28-71), BRCA1-AB: 46.7 (37-59); BRCA2-BM: 36.6 (31-52) and BRCA1-BM:42.5 (30-55). Isolated BM was observed in 7 BRCA2 cases and 2 BRCA1 cases. Most of women submitted to BA, also underwent total hysterectomy (HT): 65% for BRCA2 and 61% BRCA1. Most cases (88% non-adherent) adhere to radiological surveillance, 111/238 with annual breast S MRI and mammography. All pts submitted to BM are prescribed at least one breast MRI to check for remaining breast tissue.

CONCLUSION

Our data reveal that even if, in general, BRCA1/2 women uptake preventive surgeries at a later age that recommended, we observed a strong adherence to radiological (most with breast MRI) surveillance. BA is the PS most frequently observed but, surprisingly for healthy women, most cases also underwent TH. BRCA2 healthy women uptaken bilateral mastectomy at an earlier age than BRCA1 women. It´s possible that BRCA1 women, when deciding for BM also decided for BA.

Citation Format: Priscila Nejo, Catarina Bexiga, S. Fragoso, A Mayer, S Santos, P Louro, A Luis, C Moura, Ana Clara, Fatima Vaz. Uptake of preventive surgeries in a prospective cohort of BRCA1/2 healthy women [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-08-36.

Bioengineered adipose-derived stem cells for targeted enzyme-prodrug therapy of ovarian cancer intraperitoneal metastasis

The objective of this study was to develop a stem cell-based system for targeted suicide gene therapy of recurrent, metastatic, and unresectable ovarian cancer. Malignant cells were obtained from the ascites of a patient with advanced recurrent epithelial ovarian cancer (named OVASC-1). Cancer cells were characterized to determine the percentages of drug-resistant ALDH+ cells, MDR-1/ABCG2 overexpressing cells, and cancer stem-like cells. The sensitivity and resistance of the OVASC-1 cells and spheroids to the metabolites of three different enzyme/prodrug systems were assessed, and the most effective one was selected. Adipose-derived stem cells (ASCs) were genetically engineered to express recombinant secretory human carboxylesterase-2 and nanoluciferase genes for simultaneous disease therapy and quantitative imaging. Bioluminescent imaging, magnetic resonance imaging and immuno/histochemistry results show that the engineered ASCs actively targeted and localized at both tumor stroma and necrotic regions. This created the unique opportunity to deliver drugs to not only tumor supporting cells in the stroma, but also to cancer stem-like cells in necrotic/hypoxic regions. The statistical analysis of intraperitoneal OVASC-1 tumor burden and survival rates in mice shows that the administration of the bioengineered ASCs in combination with irinotecan prodrug in the designed sequence and timeline eradicated all intraperitoneal tumors and provided survival benefits. In contrast, treatment of the drug-resistant OVASC-1 tumors with cisplatin/paclitaxel (standard-of-care) did not have any statistically significant benefit. The histopathology and hematology results do not show any toxicity to major peritoneal organs. Our toxicity data in combination with efficacy outcomes delineate a nonsurgical and targeted stem cell-based approach to overcoming drug resistance in recurrent metastatic ovarian cancer.

16q22.1 microdeletion and anticipatory guidance

The widespread availability of comparative genomic hybridization (CGH) array analysis has led to the discovery of several genomic microdeletion-associated syndromes and has identified possible genetic causes for patients with previously unexplained clinical features. We report the case of four unrelated patients who share common clinical characteristics, namely failure to thrive, developmental delay, dysmorphic features, and congenital anomalies. CGH array analysis revealed that all four patients had a de novo microdeletion at 16q22.1. In this case report, we describe the clinical features of these patients and offer possible explanations for how their 16q22.1 microdeletion may account for their symptoms. We also suggest guidelines for the management of 16q22.1 microdeletion based on the phenotypes seen in our patients and the function of the genes affected by this microdeletion.

Reciprocal nerve staining (RNS) for the concurrent detection of choline acetyltransferase and myelin basic protein on paraffin-embedded sections

BACKGROUND

Objective of our work was to develop a sequential double nonfluorescent immunostaining method which allows the selective identification of myelinated motor fibers in paraffin-embedded samples of peripheral nerves. Motor recovery after a nerve gap-lesion repaired by artificial nerve-guides ("conduits") is often less complete and slower than sensory recovery. The mechanism for this is not fully understood.

NEW METHOD

Incubation in sheep polyclonal choline acetyltransferase antibody (Abcam 18,736) at dilution of 1:150 was followed by incubation in mouse monoclonal anti-myelin basic protein antibody (Abcam 62,631) at a dilution of 1:5000. Counterstaining was performed with hematoxylin QS (Vector Labs H-3404).

RESULTS

Immunostaining of choline acetyltransferase and myelin basic protein can be combined together and results show a good contrast between the light brown of the choline acetyltransferase reaction product and the green of myelin basic protein reaction product. Cell nuclei are stained blue. This new protocol retains the advantages of paraffin embedded sections such as (i) having a relatively simple methodology, (ii) years-long storage life, and (iii) easy sharing among laboratories. Comparison with existing method. This specific combinatorial protocol has never been used before on paraffin embedded sections. It has been named "reciprocal nerve staining" (RNS).

CONCLUSIONS

Routine combination of choline acetyltransferase and myelin basic protein immunostaining provides a highly specific, highly contrasted paraffin-embedded sections where optical differentiation of myelinated motor fibers is easy and straightforward. This method will likely simplify and speed-up the routine histological study of nerve regeneration and will contribute a better identification of the nerve motor component.

Clinical features associated with CTNNB1 de novo loss of function mutations in ten individuals

Loss of function mutations in CTNNB1 have been reported in individuals with intellectual disability [MIM #615075] associated with peripheral spasticity, microcephaly and central hypotonia, suggesting a recognisable phenotype associated with haploinsufficiency for this gene. Trio based whole exome sequencing via the Deciphering Developmental Disorders (DDD) study has identified eleven further individuals with de novo loss of function mutations in CTNNB1. Here we report detailed phenotypic information on ten of these. We confirm the features that have been previously described and further delineate the skin and hair findings, including fair skin and fair and sparse hair with unusual patterning.

Phenotyping GABA transaminase deficiency: a case description and literature review

Gamma-aminobutyric acid transaminase (GABA-T) deficiency is an autosomal recessive disorder reported in only three unrelated families. It is caused by mutations in the ABAT gene, which encodes 4-aminobutyrate transaminase, an enzyme of GABA catabolism and mitochondrial nucleoside salvage. We report the case of a boy, deceased at 12 months of age, with early-onset epileptic encephalopathy, severe psychomotor retardation, hypotonia, lower-limb hyporeflexia, central hypoventilation, and rapid increase in weight and, to a lesser rate, length and head circumference. He presented signs of premature pubarche, thermal instability, and water-electrolyte imbalance. Serum total testosterone was elevated (43.3 ng/dl; normal range <16), as well as serum growth hormone (7.7 ng/ml; normal range <1). Brain magnetic resonance imaging (MRI) showed decreased myelination and generalized brain atrophy, later confirmed by post-mortem examination. ABAT gene sequencing was performed post-mortem, identifying a homozygous variant c.888G > T (p.Gln296His),not previously described. In vitro analysis concluded that this variant is pathogenic. The clinical features of this patient are similar to those reported so far in GABA-T deficiency. However, distinct mutations may have a different effect on enzymatic activity, which potentially could lead to a variable clinical outcome. Clinical investigation aiming for a diagnosis should not end with the patient's death, as it may allow a more precise genetic counselling for the family.

Further delineation of the KBG syndrome phenotype caused by ANKRD11 aberrations

Loss-of-function variants in ANKRD11 were identified as the cause of KBG syndrome, an autosomal dominant syndrome with specific dental, neurobehavioural, craniofacial and skeletal anomalies. We present the largest cohort of KBG syndrome cases confirmed by ANKRD11 variants reported so far, consisting of 20 patients from 13 families. Sixteen patients were molecularly diagnosed by Sanger sequencing of ANKRD11, one familial case and three sporadic patients were diagnosed through whole-exome sequencing and one patient was identified through genomewide array analysis. All patients were evaluated by a clinical geneticist. Detailed orofacial phenotyping, including orthodontic evaluation, intra-oral photographs and orthopantomograms, was performed in 10 patients and revealed besides the hallmark feature of macrodontia of central upper incisors, several additional dental anomalies as oligodontia, talon cusps and macrodontia of other teeth. Three-dimensional (3D) stereophotogrammetry was performed in 14 patients and 3D analysis of patients compared with controls showed consistent facial dysmorphisms comprising a bulbous nasal tip, upturned nose with a broad base and a round or triangular face. Many patients exhibited neurobehavioural problems, such as autism spectrum disorder or hyperactivity. One-third of patients presented with (conductive) hearing loss. Congenital heart defects, velopharyngeal insufficiency and hip anomalies were less frequent. On the basis of our observations, we recommend cardiac assessment in children and regular hearing tests in all individuals with a molecular diagnosis of KBG syndrome. As ANKRD11 is a relatively common gene in which sequence variants have been identified in individuals with neurodevelopmental disorders, it seems an important contributor to the aetiology of both sporadic and familial cases.

Detection of change in fluorescence between reactive cyan and the yellow fluorophores using a-SiC:H multilayer transducers

Optical colour sensors based on multilayered a-SiC:H heterostructures can act as voltage controlled optical filters in the visible range. In this article we investigate the application of these structures for Fluorescence Resonance Energy Transfer (FRET) detection, The characteristics of a-SiC:H multilayered structure are studied both theoretically and experimentally in several wavelengths corresponding to different fluorophores. The tunable optical p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructures were produced by PECVD and tested for a proper fine tuning in the violet, cyan and yellow wavelengths. The devices were characterized through transmittance and spectral response measurements, under different electrical bias and frequencies. Violet, cyan and yellow signals were applied in simultaneous and results have shown that they can be recovered under suitable applied bias. A theoretical analysis supported by numerical simulation is presented.

Multilayer architectures based on a-SiC:H material: tunable wavelength filters in optical processing devices

The characteristics of tunable wavelength filters based on a-SiC:H multilayered stacked pin cells are studied both theoretically and experimentally. The optical transducers were produced by PECVD and tested for a proper fine tuning of the cyan and yellow fluorescent proteins emission. The active device consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructures sandwiched between two transparent contacts. Experimental data on spectral response analysis, current-voltage characteristics and color and transmission rate discrimination are reported. Cyan and yellow fluorescent input channels were transmitted together, each one with a specific transmission rate and different intensities. The multiplexed optical signal was analyzed by reading out, under positive and negative applied voltages, the generated photocurrents. Results show that the optimized optical transducer has the capability of combining the transient fluorescent signals onto a single output signal without losing any specificity (color and intensity). It acts as a voltage controlled optical filter: when the applied voltages are chosen appropriately the transducer can select separately the cyan and yellow channel emissions (wavelength and frequency) and also to quantify their relative intensities. A theoretical analysis supported by a numerical simulation is presented.

Semiconductor device as optical demultiplexer for short range optical communications

In this paper we present results on the use of a multilayered a-SiC:H heterostructure as a wavelength-division demultiplexing device for the visible light spectrum. The proposed device is composed of two stacked p-i-n photodiodes with intrinsic absorber regions adjusted to short and long wavelength absorption and carrier collection. An optoelectronic characterisation of the device was performed in the visible spectrum. Demonstration of the device functionality for WDM applications was done with three different input channels covering the long, the medium and the short wavelengths in the visible range. The recovery of the input channels is explained using the photo-current spectral dependence on the applied voltage. An electrical model of the WDM device is proposed and supported by the solution of the respective circuit equations. Short range optical communications constitute the major application field, however other applications are also foreseen.

Photocurrent and spectral response analysis of a-SiC:H pinip and pinpin photodiodes

We present in this paper results about the analysis of photocurrent and spectral response in a-SiC:H/a-Si:H pinpin and pinip structures. Our experiments and analysis reveal the photocurrent profile to have a strong nonlinear dependence on the externally applied bias and on the light absorption profile, i.e., on the incident light wavelength and intensity. Our interpretation points out the cause of such effect to a self biasing of the junctions under certain unbalanced light generation of carriers and to an asymmetric reaction of the internal electric fields to the externally imposed bias. The possibility to relate such a behavior to the light intensity and wavelength indicates realistic hypothesis of using these structures and this effect for color recognition sensors. We present results about the experimental characterization of the structures and numerical simulations obtained with the program ASCA. Considerations about electrical field profiles and inversion layers will be taken into account to explain the optical and voltage bias dependence of the spectral response. Our results show that in both structures the application of an external electrical bias (forward or reverse) mainly influences the field distribution within the less photo excited sub-cell.

Pinpi'n and pinpii'n multilayer devices with voltage controlled optical readout

In this paper we present results on the optimization of a pinpii'n type a-Si:H based three color detector with voltage controlled spectral sensitivity. The sensor element consists on a glass/ITO/p-i-n a-SiC:H multilayer structure which faces the incident illumination, followed by a-SiC:H(-p)/a-SiC:H(-i)/Si:H(-i')/SiC:H(-n)/ITO heterostructure, that allows the optically addressed readout. Results show that this approach leads to regionally different collection parameters resulting in multispectral photodiodes, coding for red (R), blue (B), and two green (G) components. In the polychromatic operation mode different sensitivity ranges are selected by switching between different biases so that the basic colors can be resolved with a single device. Positive bias is needed under blue irradiation and moderate reverse bias under green. The threshold voltage between green and red sensitivity depends on the thickness of the bottom a-SiC:H (-i) layer, and corresponds to the complete confinement of the absorbed green photons across the pinpi sequence. As the thickness of the a-Si:H i'-layer increases, the self-reverse effect due to the front absorption will be balanced by the decrease of the self-forward effect due to the back absorption shifting the threshold voltage to lower reverse bias. The various design parameters are discussed and supported by a numerical simulation.

Modeling a-SiC:H tandem pinpin and pinip photodiodes for color sensor application

The present paper reports the optical properties of multilayer structures composed by p-i-n cells based on a-SiC:H or a-Si:H material. Different structures are studied in order to obtain image sensors that accomplish color filtering in addition to image pattern recognition. A simple theoretical model is developed to explain sensors behavior and to derive the optical-readout experimental procedure. Electrical models for the sensors are established for simulation purposes and to compare photocurrent signals with experimental data. A numerical simulation of the JV characteristic and of the spectral response is also presented in order to show possible future optimization of the device. Two main structures are studied, namely p-i-n/p-i-n and p-i-n/n-i-p tandem cells.