"Precise Prediction of Fruit 'Dangdo': KAIST Develops Portable Spectrometer"

by Jeong Ilwoong

Published 24 Oct.2023 08:29(KST)

A portable spectroscopic sensor capable of precisely predicting fruit sugar content has been developed. Its small, convenient size and accurate sugar content prediction are expected to enhance its usability in the field.

KAIST announced on the 24th that Professor Ki-Hoon Jeong's research team from the Department of Bio and Brain Engineering has succeeded in developing a high-resolution portable spectroscopic sensor.

Provided by KAIST

Typically, spectroscopy measures the wavelength distribution of light reflected or absorbed by a substance, allowing analysis of its unique components. This advantage has led to its active use as a non-destructive sample analysis technique in various application fields.

However, existing commercial spectrometers, while capable of providing real-time component analysis, have limitations due to their large system size, making them difficult to carry or use for on-site diagnostics.

Recently, thanks to advances in micro-nanofabrication technology, compact spectroscopic sensors have been developed and are being utilized in quality evaluation, environmental monitoring, placebo diagnosis, and healthcare.

Nonetheless, current compact spectroscopic sensors suffer from reduced optical performance due to simplification of internal optical components, resulting in lower accuracy in sample analysis. This motivated the development of technology to reduce size without degrading optical performance.

To address this issue, the research team first proposed a solid immersion diffraction grating structure, where visible light entering a spectrometer just a few millimeters thick passes through a diffraction grating fabricated inside quartz, dispersing widely over a short distance.

They also bonded a lens with a refractive index similar to the diffraction grating, designing it so that the dispersed light forms a flat focus on the image sensor, achieving uniform spectral resolution across the entire visible light range.

Through this, the micro spectrometer module developed by the team measures 8 mm × 12.5 mm × 15 mm in size.

This represents a reduction of more than 1000 times compared to existing commercial spectrometers, with a high resolution averaging 5.8 nm and high sensitivity exceeding 76% within the operating wavelength range, comparable to commercial spectrometers, which are considered its greatest advantages.

Provided by KAIST

Previously, to experimentally verify applications of the micro spectrometer module, the research team designed and fabricated a portable spectroscopic sensor and conducted quality verification of fruit, one of the most representative cases in spectroscopic applications.

In this process, the team attached the developed spectroscopic sensor to the surface of fruit to easily acquire spectral signals. By analyzing the shape of the spectral signals, they predicted the fruit’s ripeness and compared it with actual ripeness, establishing a highly reliable prediction model with a correlation coefficient above 0.91.

Through this, the team explained that the degradation of optical performance seen in existing compact spectrometers was resolved by the micro spectrometer with a solid immersion diffraction grating structure, confirming the feasibility of using the portable spectroscopic sensor for on-site diagnostics.

Professor Ki-Hoon Jeong emphasized, “The micro spectrometer developed by our team can be an important tool not only for food and beverage quality inspection but also in fields requiring on-site inspection and diagnosis such as agriculture, fisheries, healthcare, and in pharmaceutical, bio, and semiconductor inspection fields that require high-speed quality analysis.”

Meanwhile, this research was led by PhD candidate Jung-Woo Park from KAIST’s Department of Bio and Brain Engineering, supported by the Ministry of Science and ICT, the Pan-Government Medical Device R&D Project Group Foundation, and PiQuant Co., Ltd.