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Titanium dioxide/zinc telluride/Aluminium antimonide-assisted Label-free Plasmonic sensor for early detection of Glucose in Urine

This paper proposes and numerically validates a high-performance, label-free surface plasmon resonance sensor utilizing a multi-layered structure of silver, titanium dioxide, zinc telluride, and aluminium antimonide to achieve exceptional sensitivity and resolution for the early detection of glucose in urine.

Original authors: Manikanta Jetti, Sandeep Boddu, Yesudasu Vasimalla, Suman Maloji, Santosh Kumar

Published 2026-07-04

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CC BY 4.0

Original authors: Manikanta Jetti, Sandeep Boddu, Yesudasu Vasimalla, Suman Maloji, Santosh Kumar

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are trying to detect a tiny drop of sugar in a glass of water, but you can't taste it, and you can't see it. In the medical world, this is like checking for diabetes by looking for glucose in urine. The paper you provided describes a new, super-sensitive "electronic nose" designed specifically to sniff out this sugar without needing any chemical labels or dyes.

Here is a breakdown of how this sensor works, using simple analogies:

The Big Idea: A Musical Tuning Fork

Think of the sensor as a very precise musical instrument. In physics, there's a phenomenon called Surface Plasmon Resonance (SPR). You can imagine this like a tuning fork. When you hit a tuning fork at just the right pitch, it vibrates loudly.

In this sensor, instead of sound, we use light.

The Prism (The Tuner): The device starts with a special glass block (a K108 prism). It shoots a beam of red light (633 nm wavelength) into the glass.
The Metal Layer (The String): On top of the glass, there is a very thin sheet of Silver (Ag). This acts like the string of the instrument. When the light hits the silver at a perfect angle, it creates a ripple of energy called a "surface plasmon wave."
The Sweet Spot: When the light hits the silver at the exact right angle, the energy transfers into the wave, and the light disappears (the reflection drops to near zero). This is the "resonance."

The Problem: The Signal is Faint

In older sensors, this "sweet spot" was a bit blurry. If you added a little sugar to the urine, the angle where the light disappeared would shift, but the shift was small and hard to measure accurately. It was like trying to hear a whisper in a noisy room.

The Solution: The "Super-Stack"

To make the sensor much sharper and more sensitive, the authors built a multi-layered sandwich on top of the silver. Think of this as adding a high-tech amplifier to the tuning fork.

Titanium Dioxide ( $TiO_2$ ): This is the first layer. It's like a tightening clamp. It squeezes the light energy closer to the surface, making the wave more intense.
Zinc Telluride (ZnTe): This is the second layer. It acts like a magnifying glass, further focusing the light and helping it interact more strongly with whatever is on top of it.
Aluminium Antimonide (AlSb): This is the final, crucial layer. It's the specialized antenna. This material is excellent at interacting with light and is very sensitive to changes in the environment.

How It Detects Glucose

When you place a drop of urine on this sensor:

Normal Urine (Low Sugar): The light hits the silver at a specific angle (let's say 81.5 degrees) to create that "disappearing act."
Diabetic Urine (High Sugar): Sugar changes the "thickness" or density of the liquid (technically called the Refractive Index). This tiny change messes with the light wave.
The Result: Because of the "Super-Stack" layers, the sensor is so sensitive that even a tiny bit of sugar forces the light to hit the silver at a completely different angle (shifting to 86.5 degrees) to make the light disappear again.

The authors found that this new design is 416.42 degrees per unit of refractive index sensitive. To put that in perspective, it's like the sensor can hear a whisper from across the room, whereas older sensors could only hear it if you were right next to them.

The "Recipe" for Building It

The paper also outlines how to actually build this thing, step-by-step:

Clean the Glass: Wash the prism with alcohol and water.
Spray the Silver: Use a vacuum machine to coat it with a 56-nanometer layer of silver (thinner than a human hair).
Add the Layers:
- Coat with 8nm of Titanium Dioxide (using a special atomic layer process).
- Add 1nm of Zinc Telluride.
- Finally, add a single atomic layer of Aluminium Antimonide.
Test It: Flow urine samples over the surface and watch the angle of the light shift.

The Bottom Line

The authors claim this new "sandwich" sensor is significantly better than previous designs. It doesn't just detect glucose; it does so with a Quality Factor (sharpness of the signal) of 142.28, which is much higher than other sensors they compared it to.

In short, they built a highly tuned, multi-layered light detector that can spot the difference between healthy and diabetic urine by measuring how much the angle of a light beam needs to change to "tune out" the signal. It's a label-free, non-invasive way to catch diabetes early, based entirely on the physics of light and special materials.

Technical Summary: Titanium Dioxide/Zinc Telluride/Aluminium Antimonide-Assisted Label-Free Plasmonic Sensor for Early Detection of Glucose in Urine

Problem Statement
The detection of glucose in urine is a critical component in managing metabolic disorders and diabetes mellitus. While conventional methods such as copper salt reduction, enzymatic strips (e.g., Clinistix, Diastix), and the hexokinase method exist, they often suffer from limitations including interference by other urinary constituents (uric acid, creatinine, ascorbic acid), lack of specificity, and the need for invasive blood sampling in some contexts. Although non-invasive optical techniques like Surface Plasmon Resonance (SPR) have emerged, traditional single-metal-layer SPR sensors often face challenges regarding resonance sharpness, sensitivity, and the durability of materials (e.g., silver oxidation or the instability of black phosphorus and MXene in aqueous environments). There is a continued need for highly sensitive, stable, and label-free biosensors capable of real-time, non-invasive glucose monitoring with improved resolution.

Methodology
The authors propose a multi-layered SPR sensor designed using the Kretschmann configuration. The sensor structure consists of a K108 (LZOS) prism, a silver (Ag) metallic layer, and a stack of dielectric and semiconducting layers: Titanium Dioxide ( $TiO_2$ ), Zinc Telluride (ZnTe), and Aluminium Antimonide (AlSb).

Modeling: The optical response of the sensor is modeled using the Transfer Matrix Method (TMM) at a wavelength of 633 nm. The simulation employs angular interrogation to analyze the reflectance versus the angle of incidence.
Material Selection:
- Ag: Chosen for its strong plasmonic character and ability to excite surface plasmon polaritons (SPPs).
- $TiO_2$ : Selected for its high refractive index (2.5836), large bandgap, and chemical stability to prevent metal oxidation and enhance light trapping.
- ZnTe: Utilized for its high refractive index (2.9887) and efficient wave-guiding properties to increase refractive area confinement.
- AlSb: Introduced as an active sensing layer (a 2D material candidate) to enhance sensitivity and specificity through strong light-matter interaction and high carrier mobility.
Optimization: The study systematically optimized the thickness of each layer. The Ag layer thickness was varied from 40 to 56 nm, followed by optimization of the $TiO_2$ thickness (1–8 nm) and ZnTe thickness (1 nm). Finally, the performance of different 2D materials (AlSb, Black Phosphorus, Graphene, $WS_2$ ) was compared to determine the optimal top layer.
Analyte: The sensing medium simulates urine samples with glucose concentrations corresponding to refractive indices (RI) ranging from 1.335 (non-diabetic) to 1.347 (highly diabetic).

Key Contributions

Novel Heterostructure: The paper introduces a specific multilayer configuration (K108/Ag/ $TiO_2$ /ZnTe/AlSb) designed to overcome the stability and sensitivity limitations of previous SPR biosensors.
Material Synergy: The study demonstrates the synergistic effect of combining dielectric ( $TiO_2$ , ZnTe) and semiconducting (AlSb) layers to enhance plasmonic confinement and field interaction at the sensing interface.
Comprehensive Optimization: Through iterative simulation, the authors identified the optimal layer thicknesses (Ag: 56 nm, $TiO_2$ : 8 nm, ZnTe: 1 nm, AlSb: 0.53 nm) to maximize sensor performance.
Comparative Analysis: The proposed design is rigorously compared against previously reported SPR sensors for urine glucose detection, highlighting significant improvements in sensitivity and quality factors.
Fabrication Roadmap: The paper outlines a standard, step-by-step fabrication process involving electron-beam deposition, Atomic Layer Deposition (ALD), Physical Vapor Deposition (PVD), and Chemical Vapor Deposition (CVD), suggesting the design is feasible for experimental realization.

Results
The numerical simulations based on the TMM yielded the following performance metrics for the optimized K108/Ag/ $TiO_2$ /ZnTe/AlSb structure:

Sensitivity: A maximum sensitivity of 416.42°/RIU was achieved at an RI of 1.347. This represents a significant increase compared to the baseline structures (S1–S4) and outperforms many previously reported designs.
Quality Factor (QF): The sensor achieved a QF of 142.28 RIU⁻¹, indicating sharp resonance characteristics.
Figure of Merit (FoM): The FoM was calculated at 129.07.
Signal-to-Noise Ratio (SNR): The SNR reached 1.707 at the highest RI.
Combined Sensitivity Factor (CSF): A value of 91.18 was recorded.
Resonance Shift: The optimized structure exhibited a maximum resonance angle shift ( $\nabla\theta_{res}$ ) of 4.997° for the RI change from 1.335 to 1.347.

In comparative studies, the proposed sensor (416.42°/RIU) demonstrated higher sensitivity than recent works utilizing structures such as BK7/Au/Ag/AlN/BP (394.44°/RIU) and BK7/Ag/ZnSe (366°/RIU).

Significance and Claims
The authors claim that the integration of $TiO_2$ , ZnTe, and AlSb significantly enhances the plasmonic behavior of the sensor, offering a substantial improvement over traditional SPR biosensors. The study posits that the proposed design provides:

High Resolution: Evidenced by the sharp resonance curves and high QF.
Stability: The use of chemically stable dielectric layers protects the silver from oxidation, addressing a common durability issue in biofluid sensing.
Label-Free Detection: The sensor operates without the need for fluorescent or radioactive labels, suitable for real-time monitoring.
Clinical Applicability: The sensor is presented as a viable tool for the early, non-invasive detection of glucose in urine, potentially aiding in the diagnosis and management of pre-diabetic and early-diabetic states.

The paper concludes that the proposed structure, supported by a clear fabrication protocol, represents a promising strategy for developing cost-effective and accurate biomedical diagnostic tools for glucose monitoring.