Quantum Dots for Margin Visualization in Non-Melanoma Skin Cancers: Advances in Nanotechnology for Cutaneous Surgical Precision

Introduction

Non-melanoma skin cancers (NMSCs), primarily basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), constitute over 95% of all skin cancers and are the most commonly diagnosed malignancies worldwide [1]. While BCC is typically indolent, SCC carries a higher risk of local invasion and metastasis, with rising incidence projections across aging and sun-exposed populations [1,2]. The primary treatment for NMSC remains surgical excision, where complete removal with histologically negative margins is critical for curative outcomes. Despite advances in surgical dermatology, margin delineation during excision remains challenging. Conventional approaches such as frozen section analysis, dermoscopy, and Mohs micrographic surgery (MMS) offer varying levels of precision but suffer from drawbacks including sampling errors, procedural complexity, high costs, or limited intraoperative visualization [3,4]. There is an unmet need for real-time, high-resolution tools that can reliably highlight tumor borders during excision, especially in cosmetically and functionally sensitive areas. Quantum dots (QDs), semiconductor nanocrystals with tunable fluorescence, represent a transformative platform for surgical margin visualization. Their unique optical characteristics include size-dependent emission wavelengths, high quantum yield, narrow emission spectra, broad excitation profiles, and exceptional photostability [5,6]. These properties allow for deep tissue penetration using near-infrared (NIR) fluorescence, multiplex imaging of tumor markers, and minimized background autofluorescence, features particularly advantageous for intraoperative guidance in cutaneous oncology (Figure 1). In the context of NMSC, QDs can be functionalized with monoclonal antibodies, peptides (e.g., RGD or A20FMDV2), or aptamers targeting overexpressed biomarkers such as EGFR, αvβ3, and αvβ6 integrins [7-10]. These conjugates enable real- time fluorescent labeling of tumor margins, even within complex tissue environments or 3D tumor spheroids [11]. Furthermore, innovations in QD delivery, such as microneedles, stem cell vehicles, and liposomal encapsulation, enhance tumor selectivity while minimizing systemic exposure [12,13]. Emerging preclinical evidence now supports the feasibility of QD-guided margin visualization in NMSC, offering spatial resolution in the range of 20–100 µm [3,4]. This review synthesizes current data on QD formulations, targeting ligands, delivery strategies, and clinical translation potential, and highlights how QDs may improve intraoperative precision and long-term oncologic outcomes in cutaneous oncology.

Schematic illustration of a quantum dot (QD) platform for surgical margin visualization in non-melanoma skin cancers. QDs (e.g., CdSe/ZnS, InP/ZnS) are surface-functionalized with ligands such as EGFR monoclonal antibodies, RGD peptides, or A20 peptides for selective binding to tumor-associated markers. These nanoconjugates can be delivered via intravenous injection, mesenchymal stem cell carriers, or microneedle arrays. Upon binding to tumor margins, QDs emit near-infrared (NIR) fluorescence, enabling real-time intraoperative guidance and precision excision.

Physicochemical Properties of Quantum Dots
QDs are semiconductor nanocrystals, typically ranging from 2 to 10 nanometers in diameter, whose optical and electronic properties are dictated by their size and composition. Their design can be customized to meet the demanding requirements of surgical oncology, especially for real-time, high-contrast visualization of non-melanoma skin cancer (NMSC) margins.

Composition and Core–Shell Architecture
Most QDs used for biomedical imaging are composed of a heavy metal core such as cadmium selenide (CdSe), cadmium telluride (CdTe), or indium phosphide (InP), surrounded by a stabilizing shell like zinc sulfide (ZnS) or zinc selenide (ZnSe). This core– shell architecture enhances photostability and reduces toxic metal ion leakage [5,6]. For example, QD800 nanoparticles composed of a CdSe/CdTe core with a ZnS shell have been successfully conjugated to EGFR antibodies for in vivo imaging of SCC margins [8]. To improve safety, cadmium-free alternatives like ZnCuInSe/ZnS have emerged, offering comparable brightness and longer circulation times with reduced cytotoxicity [10]. Surface functionalization further tailors QDs for biomedical use. Common coatings include polyethylene glycol (PEG), sulfobetaine polymers, and amphiphilic lipids, which increase water solubility, reduce aggregation, and enable ligand attachment [7,14]. The net surface charge, especially positive zeta potentials, can influence non-specific cellular uptake, as demonstrated in 3D models of HNSCC spheroids [11].

Photostability and Fluorescence Quantum Yield
A defining feature of QDs is their superior photostability. Unlike traditional organic dyes that rapidly photobleach, QDs can emit strong fluorescence signals for extended imaging periods, even under prolonged excitation. This property enables continuous intraoperative visualization without signal loss [6,15]. Quantum yield, the efficiency of photon emission following excitation, can exceed 50% for many core–shell QDs, making them among the brightest fluorophores available for biomedical use [5,16]. This brightness is preserved even in tissue-dense environments, facilitating deeper signal penetration when operating in the near- infrared (NIR) range (~700–800 nm). For instance, QD800 and ZnCuInSe/ZnS QDs exhibit high signal-to-noise ratios when applied to SCC tumor models, enhancing visualization of tumor– stroma interfaces [9,10].

 Multiplexing Capacity for Multi-Marker Imaging
QDs can be engineered to emit distinct colors based on their core size and composition, allowing simultaneous detection of multiple tumor biomarkers in a single imaging session (Table 1). This multiplexing capability is especially advantageous in tumors with heterogeneous cellular populations or complex microenvironments. For example, Hu et al. utilized a panel of QDs (QD565–705) to map EGFR, E-cadherin, and vimentin expression in SCC tissues, achieving predictive accuracy for lymph node metastasis with area-under-the-curve (AUC) values >0.90 [4]. The broad excitation spectrum and narrow emission peaks of QDs also support spectrally resolved imaging systems, enabling precise spatial localization of multiple targets without signal overlap. When paired with computational deconvolution and time-gated imaging, QDs can outperform traditional dyes in both clarity and diagnostic value [5,7].
 

                           Table 1: Summary of Quantum Dot Design Features and Imaging Characteristics

Targeting Strategies for Skin Cancer Margins
NMSCs, including BCC and SCC, often overexpress specific surface biomarkers such as epidermal growth factor receptor (EGFR), integrins (e.g., αvβ3, αvβ6), nucleolin, and folate receptor-α, which provide a foundation for molecularly targeted imaging strategies [5,17,18]. Among these, EGFR is particularly relevant in SCC and has been effectively targeted using monoclonal antibody–conjugated QDs for real-time intraoperative imaging of tumor margins [4,8]. Bioconjugation techniques play a critical role in enabling specific tumor targeting. QDs can be functionalized with peptides (e.g., iRGD, RGD, A20FMDV2), antibodies (e.g., anti-EGFR, anti-HER2), or aptamers (e.g., AS1411 against nucleolin), facilitating either receptor-mediated endocytosis or high-affinity binding to tumor-associated antigens [7,11,16] (Table 2). In a notable example, αvβ3-integrin-targeting QDs conjugated to RGD peptides demonstrated selective tumor accumulation in head and neck squamous cell carcinoma, offering a clear analog for cutaneous SCC targeting. Similarly, EGFR-targeted QDs successfully delineated tumor boundaries in vivo within minutes of administration [8,9]. These approaches reflect the broader dichotomy between passive and active targeting. Passive targeting relies on the enhanced permeability and retention (EPR) effect that allows nanoscale agents like QDs to accumulate within tumor tissue due to leaky vasculature and poor lymphatic drainage [7]. However, passive accumulation alone may be insufficient for high-resolution margin detection. Active targeting, achieved through ligand-mediated recognition of tumor biomarkers, offers superior specificity and is more effective for distinguishing tumor periphery during surgical resection [12,17]. Emerging delivery platforms such as skin-derived mesenchymal stem cells (MSCs) have also shown promise. These cells naturally home to tumor sites and can transport QDs into the tumor microenvironment without compromising viability or migration, demonstrating a novel delivery method with potential applications in margin visualization [12]. Additionally, multifunctional QDs designed for simultaneous imaging and therapy (theranostics) have been explored in epithelial tumors, further highlighting the translational potential of these systems for NMSC [5,16]. Together, these strategies suggest that bioconjugated QDs, whether peptide-, antibody-, or aptamer-linked, offer a robust and tunable platform for precise visualization of tumor margins (Table 3). This is especially important for superficial tumors like NMSC, where maximizing tissue conservation without compromising oncologic control remains paramount.

Table 2: Biomarkers and Targeting Strategies for Quantum Dot Conjugation in NMSC

                                Table 3: Quantum Dot Platforms for Margin Visualization in Epithelial Tumors

Quantum Dot Imaging Platforms
QD-based imaging systems are emerging as transformative tools in dermatologic oncology, offering both in vivo and ex vivo platforms for enhanced tumor margin visualization. Their unmatched brightness, photostability, and multiplexing capabilities allow for dynamic imaging strategies tailored to the specific needs of skin cancer surgery. In vivo visualization leverages the fluorescence of surface-functionalized QDs administered systemically or locally to delineate tumor margins in real-time. Near-infrared QDs, such as QD800, enable deep tissue imaging with reduced background autofluorescence and have been successfully used to target integrins and EGFR in squamous cell carcinoma [8,9]. This facilitates fluorescence-guided surgery, where surgeons can visualize tumor borders intraoperatively using QD-labeled molecular markers. In murine models, EGFR-targeted QDs have demonstrated clear signal accumulation at cutaneous tumor edges within 15 minutes of injection, with optimal signal-to-noise ratios sustained up to 6 hours [8]. Ex vivo visualization platforms are equally valuable for margin assessment immediately after tissue excision. Liu et al. (2019) showed that fluorescent probes applied topically to excised NMSC specimens provided spatial resolution within 100 µm of histologically confirmed tumor margins [3]. Time-gated imaging systems, such as the LI-COR Odyssey scanner, further enhance QD signal clarity by suppressing autofluorescence and enabling spectral deconvolution, particularly when imaging cadmium- based or indium phosphide QDs. The integration of QDs with dermatoscopic and microscopic tools represents a promising frontier. QD-assisted fluorescence dermatoscopy could improve early diagnostic sensitivity for subclinical BCC and SCC, especially when using multiplexed QDs tuned to specific tumor and stromal biomarkers. Additionally, coupling QDs with reflectance confocal microscopy (RCM) or multiphoton fluorescence imaging allows high-resolution, depth-resolved imaging of tumor architecture, which is particularly relevant for margin control in ambiguous or infiltrative lesions. Confocal-compatible QD systems have been tested in spheroid models to visualize marker expression in live tissue analogs, and time-gated detection methods enhance visualization of QD-labeled tumor borders even in thick tissue slices [7,10]. Overall, quantum dot imaging platforms enable scalable and modular systems that can be adapted for real-time surgical navigation, rapid ex vivo pathology, and integrated preoperative mapping, all with the goal ofmaximizing precision and minimizing recurrence in NMSC resection.

Preclinical and Emerging Clinical Evidence
QDs have demonstrated strong promise in preclinical settings for delineating tumor margins in NMSC, particularly SCC and BCC (Table 4). Animal model studies, excised human specimen imaging, and comparative analyses with other fluorophores such as indocyanine green (ICG) provide converging evidence of QDs’ utility in surgical guidance. In vivo animal models have shown robust tumor labeling using QDs conjugated to EGFR antibodies or integrin-targeting peptides. In an SCC xenograft model, QD800-labeled anti-EGFR probes enabled real-time tumor margin visualization within 15 minutes post-injection [8]. Similarly, studies utilizing integrin-targeted QDs demonstrated specific accumulation in αvβ3- and αvβ6-overexpressing tumors, with significant signal enhancement and margin clarity [9,10]. Ex vivo imaging studies further support the role of QDs in surgical margin delineation. Applying a near-infrared cathepsin-activatable probe to excised SCC and BCC specimens, achieved spatial concordance with histopathologic margins within 100 µm [3]. While QDs were not used directly in the tissue samples, QD-loaded phantoms demonstrated sharper edge response and higher signal fidelity than traditional fluorescent agents, underscoring their potential in rapid intraoperative use. Comparative evaluations with standard fluorophores such as ICG reveal the advantages of QDs. ICG suffers from low photostability, rapid clearance, and broad tissue distribution, limiting its effectiveness for margin precision. QDs, in contrast, offer brighter emission, reduced photobleaching, and multiplex imaging capability [4,18]. Furthermore, time-gated detection enabled by QDs minimizes background autofluorescence and enhances tumor-to-margin contrast [10]. Collectively, these findings indicate that QDs outperform conventional contrast agents in specificity, durability, and multi-marker visualization. As cadmium-free QD formulations advance, clinical translation for real-time margin assessment during Mohs or wide local excision procedures appears increasingly feasible.
 

                                               Table 4: Delivery Strategies for Quantum Dots in Skin Cancer Models

Safety and Regulatory Considerations
Despite their promise, the clinical translation of QDs for surgical margin visualization is hindered by concerns over toxicity, biocompatibility, and regulatory approval. The heavy metal content of traditional cadmium-based QDs, such as CdSe/ZnS core–shell structures, has raised significant concerns regarding long-term tissue accumulation, oxidative stress, and potential carcinogenicity [5,6]. Studies have reported that cadmium ions released through degradation or oxidation can induce reactive oxygen species (ROS) production and mitochondrial damage, particularly in hepatic and renal systems [18]. To address these challenges, biodegradable and cadmium-free QDs are being actively developed. Carbon quantum dots (CQDs), graphene quantum dots (GQDs), and silicon-based QDs offer comparable photostability and fluorescence performance while reducing systemic toxicity [13,15]. For instance, CQDs derived from organic sources have demonstrated effective tumor labeling and minimal off-target effects in vivo, while GQDs have served as photosensitizers in photodynamic therapy with high efficacy and biocompatibility [6]. Additionally, ternary alloy QDs such as CuInSe/ZnS have been explored for their near-infrared emission and lower environmental risk [10]. Regulatory challenges remain a significant barrier to intraoperative adoption. While platforms like Cornell Dots (silica-based QDs) have progressed to clinical trials for melanoma imaging, no QD system has received full regulatory approval for surgical margin visualization in skin cancer [13]. Hurdles include stringent safety evaluations, unclear long-term biodistribution profiles, and limited standardization across imaging systems. Surface modifications such as PEGylation, zwitterionic coatings, and antibody conjugation have helped reduce immunogenicity, yet regulatory agencies continue to emphasize the need for robust pharmacokinetic, toxicity, and clearance data prior to approval [5,16].

Going forward, clinical translation will likely depend on: Transition to non-toxic, biodegradable QD systems; Integration with existing FDA-approved surgical platforms; and Evidence from large-scale animal and early-phase human studies confirming safety and accuracy. These developments are critical to ensure that QDs can move from promising preclinical tools to practical, regulatory- compliant agents for intraoperative use in dermatologic oncology.

Discussion

The next frontier in QD research for NMSC margin visualization lies in smart, multiplexed platforms that not only illuminate tumors but dynamically guide clinical decision-making. Innovations in QD design, targeting strategies, and computational integration are shaping a translational roadmap toward personalized fluorescence- guided surgery (FGS). Multiplexed QD systems, capable of emitting at distinct wavelengths, offer the ability to simultaneously label tumor cells, stromal elements, immune infiltrates, and neovasculature within a single surgical field [4,5]. For example, QDs conjugated to EGFR, αvβ6 integrin, and E-cadherin have been used to delineate cancerous epithelium, tumor-stroma interfaces, and epithelial-to-mesenchymal transition zones, providing a comprehensive tumor map in real-time [10,18]. Emerging “smart” QDs are engineered to respond to biochemical stimuli in the tumor microenvironment, such as pH changes, enzymatic activity (e.g., cathepsin cleavage), or oxidative stress, to enhance contrast only in malignant zones [3]. These context-sensitive probes could allow adaptive margin visualization, where fluorescence intensity or emission spectrum shifts based on tissue pathology, helping surgeons distinguish between inflamed, dysplastic, and malignant tissue. Integration with artificial intelligence (AI) further extends the potential of QDs beyond simple imaging. Machine learning algorithms trained on spectral and spatial data can assist in intraoperative classification of tissue types, margin adequacy prediction, and even alerting surgeons of high-risk zones in real time [13]. AI-enhanced platforms could also calibrate QD signal thresholds, minimize false-positives from autofluorescence, and enable precision resection with minimal healthy tissue loss.

Clinical translation of these tools will depend on:
•    Development of cadmium-free, FDA-compliant QDs with standardized emission profiles
•    Real-world validation in Mohs surgery and excisional procedures
•    Incorporation into AI-augmented imaging systems and portable dermatoscopic devices

In this evolving paradigm, QDs are poised not merely as fluorescent tags, but as intelligent surgical co-pilots, navigating the invisible boundaries between normal and neoplastic skin. QDs represent a transformative innovation in the visualization of surgical margins for non-melanoma skin cancers. Their unique optical properties, including high photostability, narrow emission spectra, and tunable fluorescence, make them ideal for real-time, high-resolution imaging in cutaneous oncology. Whether used in vivo during fluorescence-guided surgery or ex vivo on resected specimens, QDs offer unparalleled precision in defining tumor boundaries, potentially reducing recurrence rates and improving patient outcomes. Despite these advantages, several barriers hinder their routine clinical adoption. Concerns about heavy metal toxicity, limited regulatory frameworks, and challenges in achieving targeted delivery without off-tissue accumulation remain unresolved. Nonetheless, the development of biodegradable QDs, improved bioconjugation strategies, and integration with artificial intelligence are actively addressing these limitations. Looking ahead, QD platforms are poised to move beyond static imaging and into the realm of intelligent, multiplexed, and adaptive systems that inform surgical decisions in real time (Table 5). With continued interdisciplinary research and regulatory support, quantum dots hold significant translational promise for enhancing the precision and safety of skin cancer surgery.

                                                     Table 5: Clinical and Translational Potential of QDs in NMSC

References

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